You need to look at the Junior regulations in sequence, not in isolation.
From U11 to U13 games are started with a free pass and there is a restriction on moving before the ball is passed.
At U14 the free pass goes and is replaced by Free Kicks. The restrictions also goes.
At U15 - U18 we have Penalties added and again, no restrictions.
Finally we look at the laws of the game. There are no restrictions on a player receiving a FK or PK pass at pace.
So it is legal and allowed....unless the referee deems it dangerous, but just because one kid is bigger than another doesn't make it dangerous, because if it did where would you stop? Big kids can't tackle small kids?
U11 regs
At a free pass, the opposition must be 7 metres back from the mark. At a free pass, the passer must start with the ball in both hands and, when the referee calls “Play”, pass the ball backwards through the air to a member of their team. For safety reasons, no player from either team may run until the pass is made.
U12 regs
At a free pass, the opposition must be 7 metres back from the mark. At a free pass, the passer must start with the ball in both hands and, when the referee calls “Play”, pass the ball backwards through the air to a member of their team. For safety reasons, no player from either team may run until the pass is made.
U13 regs
At a free pass, the opposition must be 10 metres back from the mark. They cannot start moving forward until the ball leaves the hands of the passer. At a free pass, the passer must start with the ball in both hands and, when instructed by the referee who will call “Play”, pass the ball backwards through the air to a member of their team. For safety reasons, no player may run until the pass is made. The player taking the free pass must pass the ball when the referee calls “Play”
U14 regs
A free kick is a kick from hand. The kick must move the ball a visible distance out of the hand or along the ground. This can either be a tap by the player to themselves, or a kick to gain ground. The opponents must be 10 metres back, towards their own goal line and cannot start moving until the ball has been played.
U15 – U18 regs
No reference
Law of the Game
No reference
The ball must be kicked a visible distance. If the kicker is holding it, it must
clearly leave the hands. If it is on the ground, it must clearly leave the mark.
Once the kick has been successfully taken the kicker may play the ball again.