Mitsudomoe, Mitsuboshi Colors Recommendations
Trio of grade schoolers wreaks havoc in their town. They also target one older guy which they try to bully in a way. While Mitsuboshi Colors is focused on cute aspect, Mitsudomoe is focused on a bit more ecchi aspect.
Three cute girls in a cute environment messing with a grown up man.
Both series are similar in many aspects, though Mitsudomoe goes a little more ecchi.