We hatched a set of ladybugs and some butterflies. They got a kick out of watching the whole process, and we read a dozen or so books about the life cycle of both.
Ella couldn't wait to free them; Hank was really worried they'd be eaten by a wolf so it took some coaxing to get him to agree to it. Now every time we see a butterfly or ladybug, "Momma! Look! It's one of ours!" Their enthusiasm about everything is such a treat.