I agree that all Races should have children. It would be great!
Especially for adopting in Hearthfire.
Are Bethesda being supremists? or racist (if you can say that)?
Ummmm... what?
It was likely a time budget matter.
It's very time consuming to create and animate an entire new mesh. Hence, the reason why the children that are in the game basically all look the same.
They probably just ran out time, and focused on more important matters.

Also... Khajiits, Redguards, Orcs, and Argonians are rather rare in the province, so they wouldn't be bringing their kids along on a dangerous journey to a foreign province.