If you're being truthful about the content of the messages, more than likely nothing will happen at all. If for some reason Snapchat were to be alerted somehow and decided after reviewing them to send their records of the messages to a relevant task force or LEA, there's very little chance they would even pursue it if there's clearly no intent on your part to have been communicating with a minor from the beginning, and you ceased communication with them immediately when you became aware of their age.

That said, you should probably stop sending pics or your junk to people on the internet. It's never a good look if you're putting yourself in the same situation repeatedly when it involves sending illicit messages and images to minors.

In the future if this happens again (while increasingly suspicious, still plausible enough to undoubtedly be commonplace, kids are famously pretty stupid), it could actually be preferable for you to report them to Snapchat, especially if they're clearly contacting adults and requesting to either recieve or exhange illicit images, presenting themselves as an adult until after the fact.

"The first party to contact 911 is usually seen as the victim by responding law enforcement."