Surrogate child - about to be taught sex education?

I think he has a right to know. Maybe now, if you think he can handle it, otherwise maybe later. You explain the process and then say 'But you were different, you were special.'

I don't believe in talking down to kids, I talk to them like grownups (but then I don't have kids so I can't claim to be an expert). But after you go through the material with him you tell him that some women aren't able to get pregnant, to conceive, so when they want a child they find someone else to carry it. And sometimes they need someone else's egg also. So Auntie is your 'biological mother' and you are the mother who raised him and cared for him and taught him everything he knows. And of course you make sure he understand that you love him as much as if he was yours, maybe even a little more because you went to extra trouble to have him.

If you don't think he can deal with that (and you would know better than anyone) then just leave that part out. Tell him later, when he's older. I have LOTS of friends who were adopted and know it, and it didn't spoil their life to find out. Some learn very young, others later. In fact when I was in school a girl told me once 'Either my sister or I is adopted. I forget which of us.' 8^)

I would just say you came from dad and aunty helped as mummy eggs were broken but make sure he knows you both love him maybe u and ur sister can tell him together

What surgery would he need to know who his mom is? None. So just don't tell him about the surrogacy. There's no reason for him to ever know.