If you're damned if you do and damned if you don't, then the decision is easy. You say something. You give them the opportunity to get help earlier rather than later. This impacts the whole family.

It's then how you say something that counts. You may need to practice it a bit and it may depend on the situation on the day. Maybe even write a note and give it to her. Something like, I apologise if this is out of line, but I've noticed behaviour in your son that is similar to my daughter. etc etc. The reason I point this out is through experience, I know funding etc is age dependent. It is difficult to look at and I hope I'm wrong, but thought it might help...blah blah. You know better than I do what to say.

Her reaction to you is irrelevant. Just be prepared for a negative one. In this case, it's not about you, it's about the little boy and his family. You have information they need. As you're not friends, you're not risking that relationship. Just wear your protective armour that day It will take courage, but I think it's something you need to do.

GL