First i must say this is a great idea for a post! I will make a series out of it in Turkish :)

And for the important part, anything works if it contains enough proteins. There are tons of options but it does not matter if it contains different proteins. And also healthy fats.

Also the time they eat is very important. You can make them start the day early and with some healthy carbs. If they eat early, they will be very hungry for the lunch and that way it's easier for you to make them eat what you want ;)

Last but not least, don't let them eat junkfood at all! Also don't use it as a reward. Make them hate junkies if you can :D I know it's hard to do, but the devastating effects of processed foods are a serious problem. Instead make your own fruit bars, make your own chocolate at home. If they don't eat artificial sweetners, the taste of processed foods will be disgusting for them. But if you feed them with junk food early in their life, they will be addicted to sugar. Sugar addiction is a real thing! But that's another story.

To sum it up: healthy carbs, %70 protein based and full of healthy oils is the base diet. Take junks out of their reach and you are good to go.