I don't think this is as clear-cut as you write. I'm not sure what the law is in other countries, but in Poland, minors can make transactions, i.e., purchase st

I don't think this is as clear-cut as you write. I'm not sure what the law is in other countries, but in Poland, minors can make transactions, i.e., purchase stuff. This assumes that minors can consent to certain things. The burden of making sure that the transaction is fair is on the adult, and the type and value of the transaction must be adequate for the minor's age. 7yo can buy bubble gum, 12yo can purchase a book, and 17yo can purchase $60+ game. However, if an adult sells $400 laptop to 12yo, the parents of that 12yo can demand the seller to return the money to them without returning the product (ideally, they would return it), or return damaged product. The rationale is that 12yo cannot correctly handle such a valuable item, and the seller should've known better. I'm pretty sure the 12yo would not even need a receipt for the laptop - after all, the seller might not have given it to them (of course, some kind of proof would be needed). I assume similar laws exist in other countries, and hence societies recognize the capacity of minors to consent to some things.