Rant: I don't know exactly what to do.

Summer
This is going to be a little long but I need some opinions. Here it goes. My best friend for 16 years has a 3 year old that's out of control. He doesn't listen, he's not disciplined at all. He comes to my house makes huge messes. I mean huge. He once dumped an entire box of corn starch in my dogs food and water bowl then dumped it on my floor which I had to clean up. Well he's gotten to where he tries to hit my 5 month old with his hands, toys, takes things from him and breaks his stuff. I constantly get onto him and she does nothing. She is in a tough situation right now so I've been babysitting but I think I'm going to have to tell her he can't come to my house anymore. I'm sad because we are best friends, our older kids are best friends but I will not let her son hurt my baby. What would y'all do? Sorry this is so long.