I am surprised that they left it that late - most primary Year 6 classes will have at least one girl with periods and maybe even a boy with a broken voice. My lot all knew from very young, I think, but it was certainly covered in state primary in Year 5 and in some eye watering detail again in Year 6. By Year 7 I think you will be looking at stuff on contraception, s exual health and s exual orientation, as well as a video of childbirth.
I bet the 'bits and bobs' (almost misread that last word in your post) he knows might turn out to be more than you think. One of mine had conducted a thorough internet search on condoms when in Year 4. As the computer was in a 'public' space and I checked the search history, the vehement denials were futile. I did learn a thing or 2 myself about that particular market though.