Embassy Suites Hotel Downtown -- Close to both a Red line and a Blue line Metro station (the zoo is on the Red line; the Smithsonian museums are on the Blue line) and within walking distance of Georgetown, this hotel lets your kids sleep on the pullout sofa in the separate living room. Rooms have some kitchen facilities, but the complimentary breakfast in the atrium is unbelievable. There are also an indoor pool and a free game room. For all of the same reasons, but a different location (within walking distance of Penn Quarter attractions), also consider the Embassy Suites Hotel Convention Center.
Hilton Washington -- A large heated outdoor pool, three tennis courts, and a goodie bag at check-in -- what more does a kid need?
Omni Shoreham Hotel -- Adjacent to Rock Creek Park, the Omni is within walking distance of the zoo and Metro and is equipped with a large outdoor pool and kiddie pool. Children receive a goodie bag at check-in, and the concierge has a supply of board games (no charge to borrow, just remember to return).
