I have a wall where the kids drew crayon on and we've had people sign it over the years. Y'all are way too high class for me!
We have a framed "picture" - white pasteboard with several handprints from our kids when they were little. It hangs in the hall, a reminder of how time flies.
My wife was doing some project and had all the kids put paint on their hands take prints. One of her best ideas.