I built a Lego playground. The playground includes a wood lookout tower with a ladder in the back, a roundabout (The yellow spiny thing), a concession stand with an apple and 1 soda can behind the lady, a tree that provides shade for the wood bench with a lamp on the side if your mini figures are out late at night, and a sandbox ground with black barriers so the sand won't freely fall out. The mini figures include a teenage boy sitting on the park bench watching his 2 little siblings and 1 concession stand worker in green overalls.
I built this playground because I recently bought the "Fun at the Park" set with a lot of mini figures and I can build a city with it starting with a simple playground.
I think this would be a good set for smaller children ages 4-7. The set is easy to build and could be an addition to a city that other people may have already built. I think the price would be pretty cheap since it doesn't include a lot of pieces and is very small (around $15). Also this set could be a "kick-starter" to the younger folks for their future city.