"Think we're coming back here again?"  That's one of the first things we ask each other when we visit a museum or park that charges admission (not all do - like the Smithsonian in DC, the Walters and BMA in Baltimore, and others).  Seems ridiculous when we've only just gotten there, but whatever.  If it's a local science museum, art museum, or, after a couple hours, she's duct-taped herself to part of the apparatus, the answer is likely 'yeah, likely.' 

Out comes the credit card and a few days later another family membership arrives.  The math is usually pretty darn easy - two visits, especially with friends or visiting relatives, and the membership is paid off.  Rest of the year = free.  Win! 

Plus, you have something to do with visiting relatives and spare days that the kid loves, and a place to go that isn't already covered in crayon.

An extra bonus, though, is when you go visiting yourselves, and have a couple of hours to spare.  Lots of these memberships - not all, but a lot?  They transfer.  Have a membership to the Academy of Natural Sciences in Philadelphia?  Get into the Maryland Science Center for free.  Win!  Have a pass to Port Discovery in Baltimore?  The Please Touch Museum is yours.  Each museum has a list of other museums across the country with whom they exchange admission or other benefits - though not all provide full parity.  Discounts to museum shops, the cafe (you know you are going to have to go down there even though it will be the End Times), and even some extras like workshops or classes, and speed-admission lines for members and their guests are also part of the package.  Some places will discount the cost of that day's admission from your membership if you decide to join at the end of your visit.

And for your loyalty, the museum gets to purr over membership growth to its benefactors… add to its built-in audience for programs and activities… and, should you happen to have won the Lotto, hit you up to become a benefactor yourself.  Not a huge trade - and you, with the child who is now learning all about polar bears and icebergs, have the richer end of the deal. 

*Unless you're the National Aquarium in Baltimore.  Seriously, this may be the only place I continue to get a membership and also want to strangle myself each time I do it.  Why NAIB? We love you a lot, in all your fishy goodness.  Why do you make family membership harder than everyone else does?  Why do you cost twice as much as everyone else, and yet, if someone needs information or to renew, it seems like we've asked you to donate your last kidney?  We wish you would love us back, just a little.