What do I do if a young fast bowler goes over their overs limit?

Under the ECB Recreational Cricket Safety Regulations, no further play is allowed until it is resolved.

Appointed Umpire

1. The bowler's end umpire stops the game and tells the bowler and their captain (team manager in junior cricket) that the bowler has reached their limit and must stop. If an over is under way, an eligible bowler finishes it, and that over counts towards the replacement bowler's limits.
2. If they refuse: treat it as time wasting. Call dead ball if the ball is in play, tell the other umpire, give the fielding captain a first and final warning, and tell the batters.
3. If they still refuse: award 5 penalty runs to the batting side (Law 41.9).
4. If they still refuse: the team is refusing to play and the match is awarded to the opposing side (Law 16.3.1.2).

Acting Umpire: stop the game and do not continue until the bowler is replaced. If the acting umpire lets play continue, the batting captain must not allow their batters to carry on. If play doesn't resume within 15 minutes, the fielding team forfeits the match.

To prevent problems, count each fast bowler's spell and daily overs against their age (team sheets in ECB competitions show players' ages).