In domestic football matches the kids/children are usually mascots, supporters of the local team who have been chosen to lead their team out for the match. It's just a ceremonial thing but how they are chosen varies from team to team and sport to sport. For instance, to be Chelsea's mascot, you have to be aged between 6-12 but have an application sent in before 8-ish due to the length of the waiting list.
About 5 years ago there were news stories about the extortionately high prices Premier League clubs charged for kids for the privilege of being a mascot. (Everton charged £2500, allegedly) Though sometimes these are part of a corporate package, with meals and use of an executive box. Clubs like Newcastle also let the match sponsors choose the mascot (for a fee of 12.5k)
International and Champions League games have so many mascots for slightly different reasons. I think its because of the FIFA fair play initiatives, it was thought that if each player had a small child wearing the opposition's kit then there was less likely to be conflict with opposition players in the tunnel before the match. Of course, this can also have a corporate spin; in the 2006 World Cup all the child mascots were sent by McDonalds.
This answer was edited by toomanysound 181 days ago.
Reason: Rewording
