you should be able to get details from the airline itself when you confirm your meal selection (which I recommend you do, again and again and again !)- I don't know about Emirates, but BA did a passable childrens meal, although with chips and choccies which I wasn't thrilled about. I have ended up taking my own food for DS on long haul flights purely because you have to wait a while for the meal to be served and it was easier for me to give DS dinner and then get him settled sooner rather than later. But that also depends on what time you fly. HTH
TBH I'd take your own foodstuffs for all your children and not solely rely on the airline (particularly if Gate Gourmet are providing the catering for this airline).
Airline food for children is invariably dire in my experience (half frozen bread roll anyone!). Also the childrens' meals are often served only a very short time before the adult meals are brought around.
It will probably be around an hour after departure before the crew commence serving meals to pax.