Sex Ed books for adopted children

[delilabell]

Ds is 6.
Knows very basics but hasn't cottoned on that men are involved.
Life story work is soon going to be introducing idea of a birth dad (knows about birth mom) so I'd like to have a book on how babies are made ready for if/when he asks.
What I struggle with is the whole mummy daddy parts of them. I want something that doesn't use those words because I know due to ds's past it'll stress him out.
Any ideas of books?

We've got 'Let's Talk About Where Babies Come From.' The language is generally good and there's a section on adoption. We tried out quite a few from the library before we found one that was right for us as an adoptive same-sex family.