I think it’s possible that loot boxes (and real-world equivalents like trading cards) don’t violate existing anti-child-gambling laws, but if so, that’s a flaw in those laws that needs to be fixed rather than an indication that they’re totally fine and should be allowed to exist in their current form. They cost money and give an unpredictable reward where different options have different perceived value, so they’re quite clearly gambling to anyone who defines it based on its characteristics rather than an individual territory’s specific legalese.