Reuse an old tree to make a log pathway in your garden. Good use of "yard" trees and other wood that can't be milled; works much better in climates without termites. Good drainage under the log rounds will make the path last longer.
18 Popular Plants to Grow from Cuttings in the Spring
Outdoor tic tac toe using stone tiles and rocks. I would make a small garden for the kids and have this in it. Cute decor when the kids aren't playing with it. Great for when the mom is at work and the kids want to play