Is your teenage child capable enough to make snack bars for themself? If so, and if they don't already know how to do this, show them how to find recipes, show them where your baking equipment is and let them develop their baking skills. Tell them to tell you/whoever does the shopping what ingredients they'd like, and if they're reasonable, buy the ingredients.
If you have space for it, consider acquiring a bread machine and use it to make bread which is much more filling than the standard supermarket loaves. Give the job of making the bread (weighing out ingredients and pressing a few buttons) to one of the children. My kids were happy with wholemeal bread when made freshly. It keeps them satisfied for much longer than a supermarket loaf.
We use a lot of bananas, apples, peanut butter, natural or greek yoghurt and seeds, oatcakes/crackers, mixed nuts, and oats/other flaked cereals in our go-to snacks. Chicken drumsticks could make an easy snack for the non-veggie members of the family, and might be useful for lunch boxes if any of your meat eaters take lunch with them. Cheese & onion lentil bars are cheap, tasty, contain useful amounts of protein and are easy to make.
Bowls of unsalted, mixed nuts with or without dried fruits are great for snacking on and if you include some dried fruits and cheap seeds, can be a good way to increase fibre intake and variety.
Good luck with finding things that work for your family, and I hope you can get some of them to share some of the burden that comes with doing more of the food prep at home.