i hope I'm not too late to answer this question.
I don't remember, but isn't your little one on 2 injections? If you're still watching the film when he has to have his snack, have popcorn for snack.
According to my Diabetes Type 1 book, 1/2 litre/23g of popcorn has 15g of carbs. When C was on 2 injections, I made her 25g of popcorn to take to the cinema, as that was easier than buying it from there. She was quite happy with that.
Now she's on MDI, she just buys the children's box and injects for it.