Experience says child meals are the same in any class. IIRC it's normally something like nuggets, potato faces, beans, with some fruit etc.

I've been advised by crew that it's best to order the meal if you're not sure and then let them know on board that your kids might prefer something from the main menu if available. Worked for me last year when my fussy daughter decided she preferred not to have the child's meal we'd ordered and went for the fish instead.