Also at that age, it may not yet be obvious what the best position is for each player, especially if they have multiple skill sets.
A simple college football analogy is the great HS/college QB that isn't good enough to make it at the next level as a QB but has scary athletic skills and changes to WR - Anquon Boldin comes to mind as a touted HS QB that played WR at FSU and now is a pro-bowler at Arizona.
Same thing in Soccer, a kid always played a certain position because that's what he was used to, but under a new coach with different eyes and a different take on things, moves him inside/outside or offense/defense and the player has a more natural feel for the position.