The World's Ugliest Sea Creatures, which are a lot of fun if your kids don't get nightmares easily.
Advantages of this activity: 1.) your kids curl up and press into you like they used to when they were littler 2.) it's fun 3.) you both learn a lot. Plus, it's funny when your three-year-old cuddles up and says: I want to look at sharks. (Except when you're editing your novel and want your privacy—that's when you hand him a shark book.)