Whenever we hike as a family water must be involved.  Not the kind you sip necessarily, but the kind you can swim, fish and explore in.  My kids love the water feature and it makes a fine carrot to dangle out there as a reward for finishing the hike without whining.  Hard Labor Creek State Park not only has water, they have a boat ramp, dock and the lovely 275 acre Rutledge Lake.  We hiked the two 1-mile loops (Brantley and Beaverpond).  The woods are quiet and lovely here, absent are the swarms of people vyiing to see everything. The gentle topography was easily manageable for our 4 year old.  Afterwards we drove to the lake nearby and fished a bit while the kids hunted for freshwater clams.  Expect a 45 minute drive from downtown Atlanta.  Stop in the Caboose for a sandwich and a Coke in historic (but very small) Rutledge.