How Old?

This is in response to how young. My answer is quite young. We have a pool at our house and my son and his best friend are always out there using it. One day this past summer his best friend’s mom and I were in the house and we looked out, surprised to see that our sons had gone off to one side by some bushes. Obviously they thought that they couldn’t be seen, but we had a perfect view. We were both surprised to see our sons had taken off their swimsuits and were naked, and that her son was performing oral sex on my son. And they are only ten years old! Neither of us could believe it!
We both thought that they were really too young to even be interested in that sort of thing. Of course we didn’t know what to say, and we did not say anything about having observed them. We both can only assume that they have happily continued to be so indulgent with one another. But how you? Very young!