Relationship advice that I probably already know

So my fiancé and I have a 7 month old beautiful baby girl and I have recently been contacted by a woman saying that she has a little 3 year old boy by him my fiancé and I have only been together for almost 2 years. But he never mentioned any other kids. The is also another baby boy that's 6 and both of them he swears up and down that both women cheated and the kids aren't his. I just want to know what you would do in this situation. I really want him to do Dna tests. To know for sure. I think I'm more afraid of the same thing happening to me. Idk what do you think?