Legality of Gift Cards and Minors for Marketing

The vast majority of our customers are minors due to the nature of our business.

Question: Is it legal in the U.S. to offer Gift Cards to Minors who go through our course, for a friend referral?
I.E. Tell a friend, they use a code, you get the gift card?

If not, is it legal to give the gift card to the parents directly if the minor finds the referral?

If it is legal, are there any limits to the number of referrals that a minor could bring in?

Also is there any type of card that is not valid for this, I.E. Store cards vs. Visa or MasterCard Gift Cards?

Thank You.