7 is not too young to ask about "it", and if this mom was concerned about teaching her son about these issues, then she should have started before he was in school, when he'd be around other kids, who do talk. There is no one The Talk, it's an ongoing discussion, at least in all the families we know. As children get older, you can go into more detail. DD was in an age appropriate "sex ed" course a couple of years ago, when she was 5. We left the actuall sex act details for the parents to address when the child asked, but the course otherwise covered all the ways families are formed, the different kinds of families, and how babies grow before being born. After the course, DD came to me with one of our books, turned to The Page, and asked me to read it. That was at 5. Clearly 7 is not too early if the issues are addressed in an age appropriate manner.
I think it's wonderful that they are starting early on teaching about these issues. I doubt very much that they're going into "tab P goes into slot V..." detail in the classroom.