Motorized scooters are not legal on public streets, even for an adult. I live on a cul de sac and kids ride around it all day - no one complains and I doubt the police would even bother to answer a call.
I have complained about basketball hoops next to a well-traveled downhill road.
I ran afoul of this when I lived in Virginia and commuted to work on a 49cc scooter, AKA in VA law as a moped. One day I was pulled over by a Barney and he began to arrest me for driving a "motorized cycle" on a public street. I was aware of Virginia law pertaining to mopeds and was utterly perplexed until I realized he thought that my bike was a child's toy. Trying to explain the situation to the Barney was a non-starter. ("It don't got no pedals it ain't a moped" saith the ignorant Barney.) Very fortunately for me another officer pulled up who was more knowledgeable. After a brief pow-wow between the officers (which involved printouts of a PowerPoint slide deck about the difference between toy cycles and mopeds) I was allowed to leave.
Why the law is concerned with motorized toy scooters and yet permits toy bikes and toy skateboards is opaque to me.