For free things for families to do:
The free concerts and movies in the summer, though we rarely go because we get too comfortable and lazy sitting on the porch, hanging around the pool, and going to the beach. Reading at the beach very early in the morning when it's quiet. Watching the sunset every evening.
The fountain at Villages of South Walton is great when it dances to music during summer evenings, though it wasn't working last August when we were there. Kids love to run through it.
Bucket of Beignets at Flip Flops. Very inexpensive breakfast though I eat 3/4s of the beignets, leaving very little for the kids.
Getting shrimp steamed and seasoned at Goatfeathers.
Biking along 30A.