For reference, the ECB Fielding Regulations are as follows:
No young player in the Under 15 age group or younger shall be allowed to field closer than 8 yards (7.3 metres) from the middle stump, except behind the wicket on the off side, until the batsman has played at the ball.
For players in the Under 13 age group and below the distance is 11 yards (10 metres).
These minimum distances apply even if the player is wearing a helmet.
Should a young player in these age groups come within the restricted distance the umpire must stop the game immediately and instruct the fielder to move back.
In addition any young player in the Under 16 to Under 18 age groups, who has not reached the age of 18, must wear a helmet and, for boys, an abdominal protector (box) when fielding within 6 yards (5.5 metres) of the bat, except behind the wicket on the off side. Players should wear appropriate protective equipment whenever they are fielding in a position where they feel at risk.
These fielding regulations are applicable to all cricket in England and Wales.