LEGO set owner, usually, 4 letters
Optimist user, maybe, 4 letters
Tricyclist, typically, 4 letters
A crude uncouth ill-bred person lacking culture or refinement, 4 letters
A young person of either sex (between birth and puberty), 4 letters
Dora the Explorer watchers, 5 letters
Little squirts, so to speak, 5 letters
Mischievous children, 5 letters