Totally freaking out. HELP

I found out tonight that my MIL (not by blood. DH step mother.) has herpes. This woman has kissed on my son, who is now 17 months. She's never told us about this. I'm concerned because I don't know how this stuff works. Is there a chance he could have this now? I plan to call his doc in the morning but for now they are closed and I just need some advice, prayers, and whatever else yall can give me. 😰