It is not trivial to small kids. This is enough of protection. If you have dexterity and persistence to open those packs, you are old enough to not eat batteries.
You're making some pretty wild assumptions. Some adults are pretty fucking stupid too.
But the law is about child protection as far as I can tell.
If *you* are assuming that adults can be as dumb as children, then uh sure, that can be occasionally the case for some people, but from a legal standpoint, adults who act as children and can't be held responsible of what they do should usually be considered vulnerable adults and taken care of properly.
Writing laws to protect chidren and targetting adults in disguise, that would be pretty fucked up.
Not that I'm really sure what you were exactly on about though.