Keeping 'em busy—so important to us, as I've explained—gets a lot easier in the summer. If you've got any kind of yard or nearby park, there are usually at least a couple of outdoor activities that serve as stand-bys, like swing sets, bikes, sprinklers, kites, etc. (avoid sandboxes). Even better, baltimore is chock full of summer festivals and events geared for kids, and this weekend is no exception.
The Charles Village Festival runs both Saturday and Sunday, featuring two music stages (a main stage and a kids stage), a garden walk, a 5k and 1k fun run for kids, and a kids' area sponsored by Village Learning Place with games, crafts, a moon bounce, and face-painting.
Sunday is the Eco-Ride and Eco-Fair for Kayam Farm (pictured), an organic Jewish communal farm at the Pearlstone Conference and Retreat Center. It involves people riding bike routes of 6 to 62 miles to raise money for the Farm, then a fair from 12 - 3, including lots of diverse entertainment (music, dance, magic), lots of games, singing, crafts, organic and earth-friendly vendors, etc. We went last year (skipping the bike ride, obvs) and it was really fun, with a very earthy, Jewish-hippie vibe. That description may sound annoying (I say that as a full-on Jew and a semi/former/admirer-of hippie(s)), but it's really not. It's actually a really lovely, communal event.
Sunday is also the Federal Hill Jazz & Blues Wine & Art Festival, which is mostly self-descriptive except to say that it is very kid-friendly, with a "Kids Kross St." area, arts and crafts, and more.
Of course, there are always the perrenially great-for-kids activities, including the Walters, which, besides the great, often kid-friendly exhibits, has a fantastic play area on the lower level with lots of dress up stuff, puppets, puzzles, and an art room where there are facilitators to help you and are kids make great projects and bonus: FREE; Also, the Marlyland Science Center ($3 off admission before noon on Saturdays, plus the weekly egg-drop contest), Port Discovery Children's Museum, The Zoo, two Storyville locations (we LOVE Storyville), The American Visionary Art Museum (also with kid-friendly exhibits, and the treehouse/sculpture out back), the various nature centers and conservancies (Oregon Ridge, Irvine, Howard County), and—of course!— the Aquarium.