I don't see where you are from, but judging by your terminology, probably not the USA, so if I say something that isn't available to you, please forgive me.
I don't have children myself, but numerous nieces, nephews, and children of neighbors and friends.
My experience is that kids love anything that seems individual, child sized stuff goes over very well. Anything that has the appearance of looking like it is just for them. If you're thinking of a quiche, then make it in cupcake tins, ditto any other kind of savory pie.
The fruit and vegetable thing? Again, this is just my experience, but the kids I've provided for love the vegetables raw with a dip. Things like broccoli, cauliflower, carrots, celery, cut into small pieces or sticks (if you can get them those fake baby carrots go over well, but otherwise cut on the diagonal as if they were chips/crisps). If you can get your kids to go for it, make the dip yogurt based. Ditto fruit. Add honey to the dip, or use peanut butter (also goes well with the veggies).
I've yet to meet a child that likes cooked cruciferous vegetables -- broccoli, cauliflower, cabbage, etc. I liked almost everything as a child, but just the smell of these things boiled would appall me. When I was a young teen, I 'learned' that you could eat these raw with dip and, wow, what a revelation.
Even at an early age, if they are so inclined (yes, even at 4), get them involved in "helping" when you cook. I had a little sis who was an incredibly fussy eater, who loved boiled beef tongue in a horseradish gravy .... because Mom had her "help" her make it one time.
I don't know how it is where you live, but around here I see parents allowing their kids to snack constantly all day, then wonder why they don't want to eat at supper time.
Almost all kids I know of like macaroni (again, kid sized), the smaller elbow type. You can do almost anything with it, it's easy for a kid to spoon in.
Some kids have a natural affinity for breakfast foods, and since yours already like spaghetti, try carbonara on them.
You can make small pancakes (blintzes), and have a set of toppings that you like, and some that they might prefer. Again, that small size (rather than larger pancakes and such) tend to appeal to children.
Just some suggestions.