12 year old sons step mother kisses him on the lips

I need help. I don't know if anyone has any legal advice because I don't think there's anything legal I can do. My kids go over their dad's every other week. My son told me yesterday that 2 weeks ago his step mom came into his room drunk. Woke him up from his sleep and then kissed him on the lips. I called my son's dad and he KNEW about it and told me it's not that serious. She was drunk and she's been going through a lot and had a hard life. What does that have to do with going into a 12 year olds room and trying to make out with them! I don't know if there is anything that can be done legally because it's a kiss. From what he told me she had her hand on his leg but it wasn't touching any of his private area. His dad is completely down playing it and saying it's not that serious and she's not a pedophile. My dad also thinks I'm overreacting and my son got to live out every young boy's fantasy. I am upset that it not only happened but that his dad knew and also told him not to tell me because I'll bitch him out.