When in Concord, make sure to visit Walden Pond. With trails around the pond, lots of little nooks to sit put your feet in the water, and a beach equipped with lifeguards, this is the place to be if you have kids. If you have small children, bring the backpack carrier. You can do the round with a stroller, but the trail is natural (not paved) and at most points it is so narrow that only the stroller will fit, and that doesn't leave room for passerbys. Also expect to walk over roots making the trail quite bumpy. Be aware that on busy days they will close the park once it is full.