Cool take on monkey bars - they're just steps hung upside down.
Idea for the side door - garage style roller door for bringing large things out/opening up shed? DIY Modern Shed project | diyatlantamodern
Funnel Stand - for your sand box or gravel area. Experiment with pouring material through different size funnels
Simple DIY backyard toy- Pvc painted and mounted to 4x4 post. pouring pebbles sand, water, and more is so FUN! Makes fun sounds too
A balance scale stimulates children's curiosity of measuring objects. They will naturally learn what objects are heavy or light. Also, through trial and error children will teach themselves about the balance relationships between different sizes and weights of objects.
slurry chutes - tunnels, chutes, tubes, funnels - fun for any sand box or gravel area
DIY Water Wall - So much fun for your kids and something they can really help with.