Depends on what is meant by the term "sex education". It depends on how such a lesson is handled.
I had thought that parents were informed by letter or similar in advance of such lessons, and had to give their consent.
And I think it is a bit precious to feel embarassed by questions from a 9 year old.
Given the rate on unwanted pregnancies, and the age at which kids start their first sexual experiences, it does not seem unreasonable to me that they are armed as soon as practicable with the salient facts of life....