I just stayed in the Wardman Park Marriott for a conference, and I think it could be nice for families wanting to do some DC touring. It's in a residential area of DC (NW), about 4 blocks from the National Zoo (I walked over there myself - they currently have 4 cheetah cubs that are a big hit with everyone, in addition to the pandas). Lots of restaurants close by and right on the Metro. It is a full service convention hotel, so no free breakfast and normal-sized rooms - although one of my colleagues did get upgraded to a very nice suite. Rates seem pretty reasonable as well (~$140). I would just phone ahead to check on whether they are expecting a really big convention during your stay, as that would probably make the stay a little less pleasant.