Would you tell the mum her daughter is talking about sex?

My daughter is 7 years old and came home from school the other day and said something really graphic (about mummy sucking daddy's ......) that she said her friend had said. I was really taken aback and shocked by this. I mentioned it to another mum and it turns out her daughter had mentioned something about sex as well that the same girl had told her. My dilemma is; should i mention something to the mum? she is a very nice respectable lady that goes to church and is a health professional. My main worry is that this girl had over heard her parents at it, and that it might be embarrassing, my friend seems concerned though, and i feel that i would want to know if it was my daughter. What would you do?