DCA is typically very un-crowded during the non-summer months unless a special event going on at DL or one of the two-fers offers is coming to an end. Aside from the rollercoasters on the Boardwalk, the only lines in the park longer than 10 minutes are for Soarin', TOT & Grizzly Rapids (and sometimes Playhouse Disney). There also a couple of slow loaders in Bugs Land that might take some time to get on if you've got little ones with you.
The most crowded days (non-summer & non-holiday) are Saturday then Sunday then Friday.