The AR-15 is nominally chambered in .223 Remington or 5.56×45mm NATO according to Wikipedia. Although some are chambered at 0.22. But typically gun makes targeted at children are not semi-automatic which is a feature of AR-15 style rifles.

While this is partially a safety concern, I remember target shooting alternatively with a pump-action and a semi-auto and my cousin and I would be tempted to lose our temper with an evasive target and mag-dump. With the pump action I didn't have the option but to aim every time.