There is really no more effective birth control than the Museum of Natural History on a weekend afternoon. Especially late afternoon, when the kids are having their exhaustion tantrums, Mommy has resorted to ignoring them completely, and Daddy is seriously considering starting a new life in Kentucky.
Also, the new butterfly exhibit? Six bucks. For about fifteen minutes worth of stuff, and an hour-long line to even get it. We skipped it. The Smithsonian is owned by the American people, and charging admission is just plain tacky.