You should try to be more open-minded. Where I live I have proof everywhere cause it's a multicultural nation, children which doesn't have the same skin tone than their parents is common.
Some examples after a quick google :
https://brightside.me/wonder-curiosities/why-some-couples-may-have-kids-with-dif...
https://www.quora.com/How-is-skin-color-determined-in-babies-Can-white-and-black...
https://www.mirror.co.uk/news/uk-news/the-rainbow-family-three-children-with-dif...
After this whether you believe it or not doesn't concern me anymore. Have a nice day.