Here's a fun post for you: making a pizza garden. This is something my kids really enjoy, so I'm sure your kids/grandkids would have a blast doing it.
First, choose a spot that gets lots of sun - about 6-8 hours a day. Then locate the center of your garden and drive a stake into the ground. Create a circular shape by tying a rope to the stake, and then tie a stick at the other end. Have kids drag the stick through the dirt, keeping the rope tight. (This should create a circle.) Then decide what you want to grow. Of course you can't grow cheese, or dough, or pepperoni, but there are lots of other ingredients to grow. I like to grow tomatoes (Italia Pompeii or Camp Joy cherry tomatoes are good), green peppers, or if you like a little color, Jewel-toned Sweet Bells, onion, garlic, oregano (I like True Greek), and basil (I like salad leaf basil). Divide your garden into pizza slices. If you'd like, you can separate the slices with little paths in between, or use long wooden sticks to create spokes. When you are planning your slices, allow 2-4 slices for the tomatoes. Involve kids at every step of the process from planting, to watering, to harvesting. When the big day comes to make the pizza, they can help slice and chop the vegetables and herbs (if they're old enough) and then place the toppings on their pizza. Bon Appetit!