It's not Crypto gambling that should be careful, it's the parents that should be careful. Though really tbh, I'd rather allow my children to be exposed to such scenes, especially if he likes games early on, but rather control him in a limited way. Maybe even join him, as long as funds are actually available and can be controlled that is. Back then, I used to buy a lot of microtransaction stuff, but most of it came from my allowance that I saved up. Now should parents be mad about that? When the child themselves saved up to buy something? Most would probably say yes, but I'm one of the others who would rather say no.
Not that I'm saying Gambling is good or bad, but rather letting them know of its existence should be rather positive instead, so at least, YOU yourself know that your child is exposed early on, and could guide him so that he could control himself, as well as to avoid making themselves fall too deep into the gambling game.
Agree on what you said, it's the parent's guidance that is needed to avoid this kind of situation where underage are gambling because of eSports. Actually, when I'm underage, I know many schoolmates that are betting because they want to support their favorite team and sometimes I'm one of those. I can't blame my parents because they already warned me about it and the school is teaching values about do's and don'ts. I already knew that it is bad but I didn't follow and just bet because of peer pressure.
The number one cause of many bad habits to a child is because of peer pressure, even the parents have full guidance, we can't still assure the good behavior of a child. In this matter, it's a big responsibility that we should put the child in a good environment to avoid these negative behavior. We should also teach them the importance of money at an early age to realize how hard to earn those things just to survive.