I’m not sure the reason, but my guess is that a child can own a debit card, but can’t own a credit card.

Credit cards are mostly a US thing. Most other places you just use debit cards.

Credit cards are of course used worldwide but most people don’t own one and those who do use it rarely, since why would you borrow money to pay for something unless it’s an emergency or some big / long term thing (at which point an actual loan is probably better, so again CC not needed).