(Dad of 2) I think the meals are generally fine for a 10 yo. I'd ask the FA when I got on board what the choices were and maybe ask to save you one of the two if it looks like the other may be a poor choice.
I've never tried getting the snack box from the back but I think you will have to pay.
Easiest bet -splurge a little more and throw a bag of trail mix in the carry on and then just see what happens, so you can enjoy the trip