I'm not in the same boat, as my girlfriend and I used donor sperm.(Lesbian couple). However the donor conception Network offer lots of books for different scenarios under their 'Our Story' range. It might be worth a look
https://dcnetwork.org/product-category/for-children/
If not...I wonder whether it's something that could be requested?
I'm a trans dad to a one year old, I've found it very difficult to find kids book that explain it