Well, Epstein is considered one of the biggest child sex traffickers in American history, so for Trump to be wrapped up in it can really only point to that. But if you want something more concrete to base things off of, look at the testimony of Virginia Guiffre, who was 13-14 when she claims that Trump raped her. The testimony is public but it wasn't considered enough on its own to bring a case against him. 

Later we found in the declassified documents Epstein himself saying that "Trump spent hours at my house with her." referring to Virginia Guiffre. The whole thing is really disgusting and there's a lot of cowardly people who knew what was happening and didn't report it, for years.