Well if he has had the chicken pox than you should be fine. Its odd that his mother had chicken pox though, more likely she may have had shingles? Either way you were probably testing in the beginning of your pregnancy for immunity to Varicella, as for your 3 year old, are they vaccinated? If so you should be fine.
I would tell him to stay away from my house and not to come over lol
I would tell him not to come over. That's really rude your pregnant and have a child.
I would tell him not to come over. How rude of him!
I would ask him to wash his hands really well from the elbows down.. He should have been considerate enough to avoid being around you though. Make sure your family washes their hands really well several times tonight as well!