I'll +3 the concept of a bento box lunch, esp for non-sandwich eaters. No need for an actual bento box (but we loved the fun silicone dividers and hard-boiled egg molds! I'm jealous; they even have a T-Rex one now!).
A really good book for an intro is
The Just Bento Cookbook and the companion website:
https://www.justbento.com/. The website was dormant for awhile but it looks to be back a bit.
And for those who say kids won't touch this stuff, you never know til you try. If you make it fun to prepare/pack and involve them, they're much more likely to eat it. Yes, it takes time. But it's worth it: the time with your kiddos will go so quickly and you'll end up with better ingredients, at usually a cheaper price. Practice over the Summer to find what you might like and develop a routine. Good luck and good munching!