Uncle Donald's Farm in Lady Lake is supposed to be great for little kids. Also, behind the Lady Lake public library on 441 (near Guava St?) there is a really great playground. Also there is a splash pad here:
yelp.com
There is a small playground up at Lake Sumter Landing, plus there used to be a boat ride on Lake Sunter (not sure if it's still there). After the playground, we took our grands for ice cream at Kilwins in LSL and a walk along the boardwalk looking for turtles.
Mystic Ice Cream on 466A towards Fruitland Park has a really interesting interior with all sorts of kitschy things, plus great ice cream. Our grands liked it a lot. There are airboat rides around. Don't forget the nightly music & dancing at the squares. Kids seem to like it.
Okahumpka park has paved walking trails and a playground and picnic tables.