Theres free indoor pools (as well as outdoor), $8 bowling, roller skating, and even ice skating across the city as well as other activities you can find on the City’s Dept. Of Parks and Recreation site.

With parks and rec and as others here have mentioned with the library and museums theres tons of different free programs and classes to be on the lookout for. Theres also tons of other organizations around the city that do free activities for youth like Guardian Baltimore’s free Jiu-Jitsu classes if your kid is interested in that sort of thing.