Our family is planning a trip to DC to visit all the usual places, and we're wondering if museums, govt. buildings, metro, etc., will allow us to carry a toddler in a back-carrier.

Metro yes, but not in most museums. They may have strollers for visitors' use, though. Check the websites of those you are interested in, under "info for visitors" or "planning your visit" or somesuch.

For the Smithsonian, this page may help--

http://www.si.edu/Visit/Security

I've carried my babies and young toddlers in a front baby carrier (Ergo). I haven't had any problems in any museum, the metro, Capitol, Library of Congress, Pentagon etc. I am not aware of them being prohibited anywhere, but I could be wrong. Back carriers may be more a different issue since you are more likely to run into people or things. We definitely used the stroller more though, since we did so much walking and the carriers were a lot harder on the back. We found DC to be a very stroller-friendly town...and we had a side-by-side double.

Good luck!

It's been a couple of years since we used a backcarrier but I don't recall any problems using them in the museums (and I don't recall any offering strollers for visitors, but I could be wrong about that).

It seems like a toddler is going to be very large, heavy to carry on someone's back for so long - never mind how irritable s/he will be - being stuck looking at the back of someone's head. I would definitely look into renting a stroller at the various museums and sites - or bringing one with you.

A nice thing about a backcarrier (at least ours) is that it's easy to bring along even if you are not using it, so our child could walk as long as he wanted and then ride for a while. We used it almost until he was about 2 1/2 or 3 and both he and I liked it.

I did remember the National Zoo rents out something (wagons or strollers) but I think they might be the exception.