Do you have siblings with children? Become the cool uncle!

Teach them to properly build treehouses, make their own bows and arrows, do skateboard tricks, handle guns, climb trees/rooftops, do parkour, and all that crazy stuff their moms wouldn't allow. Depends on what you're into, of course.

You will get to experience them at their best, but won't have to stand them at their worst. That's when you just hand them back to their parents.