You are standing on court for an hour and are a vital component in making it all run smoothly. It is an extraordinary experience for the likes of Wimbledon ball boy Callum McDonagh, 15, and his whole family. "When my mum came to see me she just burst into tears, she was so proud," he admits.

It is a familiar tale for ball girl Josie Bryant, 14, who says her mum and brother came to watch her and it was "really cool."

I am speaking to Wimbledon first timer BBG's (ball boys and girls) Callum and Josie to highlight the efforts of these extraordinary volunteer young heroes.

They are part of a 276 strong team at this year's championships and they really are the unsung heroes.

The international tennis stars are obviously the headline act, the umpire is there to keep score and order and now AI technology keeps control of the line calls, most of the time anyway.

But there are also six young heroes like Callum and Josie on each court to keep things going very smoothly. Without them it would be a mess of stray balls - just how it looks when you pop to the local park for a game.

After a rigorous selection procedure and months of training, they are ready each morning to troop out among the crowds to keep each game rolling along nicely.

Callum, from Banstead in Surrey and Josie, from nearby Petersham, Richmond spoke to me before they headed out for a busy day on the courts on day nine of the championships.

They started their Wimbledon adventure all the way back in September with Year 10 pupil Callum attending an after school club with 50 other kids at his school The Beacon. Josie went through a similar process at Grey Court School in Richmond.

Their schools, one of 31 to supply ball boys and girls to the tournament, were able to send seven pupils along to a trial in January and Callum and Josie made the cut.

Josie explains: "I had always watched the BBGs growing up and they seemed like a different species, like robots.

"I had been to Wimbledon before with school and really liked it, so I thought this would be great for me."

All the BBGs at Wimbledon are expertly looked after by manager Sarah Goldson and her team.

They are selected from around 1,500 applicants, with 170 from Years 9 and 10 and 110 from recall applications (i.e. BBGs who have been accepted at one of the last two championships).

After making it to final selection following trials in the New Year every ball boy and girl goes through a comprehensive training programme to get them match ready for three weeks in late June and early July when Wimbledon qualifying at Roehampton and the tournament itself at SW19 begins.

From February they attend two-hour weekly training sessions at the All England Lawn Tennis Club Community Tennis Centre in Raynes Park.

Training sessions involve general fitness and movement exercises but with the added key components of being a BBG - rolling, feeding and receiving those tennis balls and developing a knowledge of the game and scoring.

After the May half term, in the run up to The Championships, the training moves to the Indoor Tennis Centre in Somerset Road. One of perhaps the key, first things these keen teenagers have to learn is to be silent.

"Yes, you are trained on that," says Josie. "And at first it is a bit creepy staying so quiet."

Training on grass itself only happens towards the end of the programme, and includes a grass court week on both the Championships courts and at the Aorangi practice area during the wild card playoffs.

Once the championships arrive, six teams of six are selected for centre and number one courts. These are usually handed out to the older BBGs who have several years of experience. The remainder also work in teams of six and rotate around the other courts.

For SW19 newbies like Josie and Callum that means they have been on the outside courts this tournament.

Like all the BBGs they are based in their own area under centre court where they have got access to plenty of food and drink throughout the day. "The food is great!" says Josie.

The teams of six work one hour on court, then go back to their base for an hour for rest and refreshment. They only find out which court they are headed to next just before they leave.

The process is understandably quite hard to keep track of so when I ask them what their first game was they can only recall: "It was court six and two gentlemen. We do so much it kind of blurs into one."

I ask them if they pay much attention to the players they are feeding balls to.

"You take it all in but then it's a new game, new face," explains Josie.

The pair covered six shifts on the first two days, with their time on court reduced to 45 minutes because of the extreme heat. The average though is three or four shifts a day.

I ask them how they felt knowing millions were watching on television around the world.

Josie says: "At the start I was focused on not looking bad on the cameras but as it has gone on you settle down and you realise it's fine and you get used to it."

All the BBGs carry around their Wimbledon water bottles attached to their Ralph Lauren uniform, which they get to keep.

On the day I watched Callum and Josie they were first in action on court 6 for a boys' singles game between Mees Rottgerring of the Netherlands and Maxwell Exted of the USA.

They were on top form for their hour stint with the pair expertly collecting and feeding balls to the players at the back of the courts. They stood dead still during points and between games and then leapt into action when a stray ball went near them.

They were literally at the players beck and call as they demanded one, two, maybe three balls at a time to serve with and then arrogantly swatted one or two away for their young helper to retrieve.

It is only when you watch what they have to do that you realise how valuable the training is. The four BBGs at the back of the court (the bases) have to receive balls from their two colleagues at the net (the centres), hold on to them, then hold their arms aloft and be alert for the player seeking the right ball.

They stand like soldiers guarding a palace in the energy-sapping sun for the whole hour with only the occasional chance to get some water from their bottles.

By the time the pair troop off court with the score 6-2, 4-3 after an hour I am thoroughly in awe of their work. I shout out "well done" and they smile as they head off for a well-deserved rest.

An hour later though, they are out again, this time for a women's doubles encounter on court 11. The BBG work just goes on and on.

For committed youngsters like Callum and Josie though it is a great life-affirming experience and something to rightly make their family and friends very proud.

"My mum and dad came and watched me. They loved it and were so proud. It also made me happy as a son" Callum explains. "My little sister is in year 7 and now she wants to do it too."

And Josie says: "My mum and my friends have a group chat to see what court I am on so they can watch me. So I think they are quite proud of me."

So what about all that school work I ask our dynamic pair? While the tournament is pretty well timed near the end of the summer test and exam term and purposefully seeks out Year 9 and 10ers with less serious demands, it does inevitably mean a few school things might be missed.

Callum, who has got his GCSEs next year, says his Wimbledon stint "hasn't really got in the way" but Josie admits missing a few end of year tests and is hoping for a reprieve from her science teacher.

"When I go back I hope they don't make me do my science test! My science teacher has been cheering me on so I am sure she will show some lenience," she says.

Both say their schools "love" the arrangement with Wimbledon and teaching staff are "cheering them on."

Callum says: "All the teachers are like 'good luck' I can't wait to see you on the telly!"

And Josie jokes: "We haven't been to school for ages so when we come back I reckon we will be signing autographs."

So have they had anything go wrong in their debut Wimbledon appearances I ask?

Josie explains: "Sometimes on court you do a bad roll and you are like 'oh my gosh everyone has seen that' "We get assessed so it's a bit like 'ooh that's not good' but you don't ever do anything so bad that you feel awful."

And how about those superstar players and their never-ending ball-related demands?

While Callum plays a straight bat and says they are all "very nice" Josie admits some have been "a bit funny."

She explains: "They expect the ball immediately but we are humans too. You just have to do the job."

She references one female player whose name she cannot remember who insisted on having the balls delivered to her from one side of the court only, causing the BBG team to have to roll all the available balls to just one member at the back of the court rather than the usual two.

"She would just watch us roll the ball across rather than just asking for it from the other base which was a bit frustrating," she admits.

But while the players might be a tad indifferent, there are rightly words of praise for the pair and the whole team from the one person that really matters - their BBG chief Sarah.

"I am really proud of them," she says. "It is good to see their confidence grow through it all. It's a really tough process to get in but they find out there are rewards at the end."

Callum, who is keen to be a footballer or sports coach one day, agrees saying: "It's a once in a lifetime opportunity so you have to go for it."

And for Josie the exciting Wimbledon experience has really got her thinking.

"It would be cool one day to be one of the important people in suits walking around here with their passes," she says. "Who knows, maybe even in charge!"

And why not. If she, Callum and the rest of the BBGs keep showing their amazing commitment and dedication there's no reason at all why they cannot be tomorrow's CEOs.