Adults will just buy them for the kids. I bet tons of stores will just ignore the law too.
Isn't this what already happens?
I remember growing up (I'm from Mexico) chips often had promos where you could find collectibles with cartoon characters in the bags [1]. The cool kids had huge stacks of these, so I begged my mom to get me chips mostly for the toy. I didn't have an allowance and my mom knew better so I never got any though.