We were in the same boat with a 5yo. Here is what worked for us usually we shared an adult CS meal, he loves pizza so we got that a couple of times. On the kids menus you'll find pizza, grilled cheese, mac & cheese and PB&J as standard items. Our little one ate all but the grilled cheese, just never ordered it or wasn't an option where we ate.
He ate mickey pasta with marinara and grated cheese on the side at Narcoossee's (we paid cash for this, not worth 2TS credits). At Coral Reef he ate his entire pizza as well as apples slices for an appetizer.
He requested the PB&J a couple of times and they are readily available.
I would say know your options at the resort CS, parks and any TS you plan to visit. For instance, I knew where we could get veggie burgers at MK. I knew we had serveral options at Columbia Harbor House (closed each time we would ave eaten there). I knew that Pizza Planey at MGM, Cool Wash at Epcot would allow him to get a pizza, only adult menu at those places. We didn't use most of those places, but I had a strategy for our key locations IF we were hungry and nearby.
If eggs are a part of the diet the kids have a breakfast platter, just decline the meats. We did this with our adult platters. There was enough to share so we never ordered him his own platter. You get 2 drinks with breakfast, so we got juice/water and he chose milk.
Bottom line we had plenty to eat and so did he. CS can be tricky as at least one stop they would not allow us to get a veggie burger as part of a kids meal, so we just got our two adult meals and shared. He acually ate my pizza and I was content with just the side salad from the combo. I hear a place like Cosmic Rays in MK is more liberal and probably would allow the veggie burger for a kids's meal.
