Grow sweet strawberry in a vertical PVC tube is great solution for small garden or yard. Vertical planter will save you a lot of space, at the same time keep plants out of reach from garden insect pests AND enable you to switch to hydroponics.
Use an old tire to create a small backyard pond. My kids, 3 sons, have been helping with yard work and planting. They keep asking for a pond. I think this is a great DIY project to do outside with them. Looks simple.