I agree with Burf. No more then 1/4" Also, when my daughter was little she had a lot of trouble choking on those Biter biscuits (teething cookies) I'd recommend breaking those up too. Don't panic if he chokes. Just quickly tilt the head back and stick your finger into his throat and scoop it out. You shouldn't pat the back it can move the piece further down the throat. Cereal is great starter food, lots of cheerios. Good luck!