How to react?

We told my stepson he’s going to have a brother and he’s really excited. My husband’s ex continues to say nasty things to us about the baby coming and I can only assume nasty things to my stepson. I don’t mind personal attacks on me because I can brush them off but I’m having a hard time holding my tongue at the nasty things about my unborn child. I’m not sure how I should react or if I should even say anything.