For older kids, I would say Kindergarten and up, the Baltimore Museum of Art is offering FREE Family Sundays! Every Sunday, beginning at 2pm, the BMA is featuring a variety of interactive activities for your artsy kids, including sketching tours, hands-on art workshops, tours and more. The museum currently has a list of activities through the month of April posted, this Sunday is "Sensational Still Life Paintings" where your children build their own still life model from everyday "found" objects and then paint it. Fun, educational, and FREE!
Like I said before, I think this is for older children, but check back every week to see if there might be something geared towards the younger crowd. If you haven't been to the BMA before it's a great art museum and it's FREE, always and all of the time! It's a very easy drive, under an hour, and located about 3 miles from the Inner Harbor. Place this one on your "To-do" list, it's worth your time!
http://www.artbma.org/index.html click on Calendar and then Family Programs for more on FREE Family Sundays.