Soldiers Delight is close by and unique.
Robert E. Lee if it hasn't been raining too much.
There are also a couple of trails near Calvert Cliffs...

Robert E. Lee can be a terrifying experience for children who are afraid of dogs/don't really care for large dogs who are off teh leash to run over and knock them down. I don't blame the dogs -- I blame the hordes of irresponsible dog owners who have ruined this park for anyone else. Beware!

Oregon Ridge is our favorite. If you are still using a stroller, there is a short paved trail. And if your kids are older, there are plenty of longer trails that are a little more challenging. As an added bonus there is a nature center with all sorts of animals too.

My kids and I love going to Oregon Ridge too (they're 5,4 and 2.5). The trail around the lake has great views and isn't too tough for them. There is one "tree bridge" (two tree trunks with a railing spanning a little ravine) that is a little tricky, but the kids feel very accomplished after crossing it. We always stop at the little nature center first and then they can be on the lookout for forest critters and certain trees or plants.

The Gunpowder River trail is really nice. It's level and flat and runs along the water for several miles. You can easily hop down to the water's edge and skip stones or throw a twig in the water and watch it go with the current. You also might catch fly fishermen (and women!) or canoers as well.