There's also nothing illegal about a 7 year old jumping into a rushing river or buying unregulated "research" chemicals on the internet. Same thing, isn't it?

The way 7 year olds are kept out of rushing rivers, or consuming black market dope, is they have a parent, guardian, foster caretaker, someone looking after them. It's illegal to neglect a child. Sending a 7 year old to buy you cigarettes arguably isn't neglect, letting them smoke cigarettes or research chemicals probably is.