This kind of activity gives my little pirate motivation to take his well-needed nap! :)
I say, "Yeah! That's neat! How about you take a nap, then we can find some rocks and glue them on paper when you wake up!"
He responds, "Okay! I need my blankie." Then, heads up the stairs to his room. Lays down, requests a song, then sleeps.
When he wakes up...we find rocks outside (even in the rain or snow), and glue them to paper (even if it only was a 2 minute activity).