I usually try to pick up some toys for my nephews well in advance of my visits. I was all prepared to give them a wooden rubber-band gun and a slingshot, which I picked up on my travels for a couple of bucks. But wouldn't you know it, I went in to lab before my flight and forgot to pack the toys. What's a scientist uncle to do?
Improvise, of course.
Truth is, there are lots of nifty "toys" just lying around the lab. I remembered making 'potions' of random liquids as a child, so I grabbed a bagful of little plastic test tubes and several of these little plastic dounces (think mortar and pestle). I demo'd it for my nephews (4 and 6) and got them excited about the idea. I suggested smashing up bugs, but both children objected on ethical grounds. Instead, we picked petals from flowers and plants of different colors and "extracted" the colored juice. The older nephew, who is quite the budding young naturalist, started a little zoo of bugs in test tubes - he even caught a baby praying mantis! It was a lot of fun and confirmed my suspicions that science is a little like playtime for adults.