Doxing a minor is legal. Sharing accurate information about someone over the internet is protected speech. Threats or repetitive contact can be bullying or harassment which are crimes. The age of the victim is only a consideration for the level of punishment.
Unsolicited Sugar Daddy requests on Instagram are from scammers. Real sugar daddies do not send requests to random people. Instead, they would use one of the various websites devoted to finding sugar babies or private referrals. You should ignore any unprovoked requests you receive from someone you do not know.