Is it legal to use a debit card of someone under the age 18 on a online betting site if the user that is betting is over 18?

When using a debit card at any reputable online betting site, they use the card information to verify the potential member's identity. The underage card holder is not eligible to sign up, nor are you able to use their card to sign up either. If you want to make a deposit, research prepaid cards that do not have an international block on them.