They're aren't they're are fining his club.
In the years I've been involved in youth football it's. Very rare for a youngster to be sent off. U16 is usually the time it takes off.
Up to the ref if he wants to let County F A know. Once he has the fine is issued to the club not the player. The club has to pay or will as a club be banned from playing. Your club can't enforce the penalty on your son but with the club I help coach we would expect the players parent to pay...