So, always check the chamber before allowing your 3 year-old to play with your weapon.
I would never give a three-year-old a semiautomatic for a toy. Their little hands aren't strong enough to rack the action back in a combat reload. You start them off with revolvers at that age, something with a nice easy trigger pull, maybe single-action only until their grip strengthens.
And no full auto before age seven. It'll give 'em something to look forward to.