What are the laws about 4-wheelers and children in Massachusetts?

[Mozz]

He rides in the yard and the field behind the yard (lots of land). He wears a helmet and safety glasses. He's 9, weighs... I dont even know (how bad a parent am I?) Live in Mass. We recently came into a 4-wheeler. I know there was a lot of talk about changing the laws so that kids couldn't ride them anymore. I didn't pay attention because it had nothing to do with me. Now I need to know and can't find any useful google results. Did the law change? What is it? Are previously purchased 4-wheelers grandfathered in? (They're made especially for kids and cost a mint.)