Answer:
5 children
Step-by-step explanation:
I think that mary have 5 children.
She has four daughters and each daughter has a brother. Mary is the mom and has four daughters and she has a son. The four daughters are siblings with one another and they have the same mother so then they would have one brother because they share a brother
(Not sure if this makes sense tried to explain a bit but it was a bit hard to explain..if wrong I'm sorry)