Hi there Jason , I totally agree that your son is not at fault, the school certainly have a lot to answer for!
With regards to the birds and the bees talk I feel it would be better coming from you his father, rather than his mother , it may be more comfortable for him .
You could wait for him to start asking you questions or you could let him know that if there is anything he wants to talk about or ask on this subject you are there for him.
Best of luck
Joanne