We see human children in skyrim but why are still no other races's children like argonians, khajiits, orcs , etc?

Orc kids would be cool.

There is an Orc librarian though... which is almost equal to that.

Because they couldn't just lift them from Fallout 3/New Vegas?

It probably wasn't worth investing the time in creating them when say a dunmer child might only be used once. Children are very rare in the game as it is, 2-3 per town at most.

Who sent people to kill me...

Orcs we could possible have'd seen.But i don't know why...and also Argonians.But not redguards and Khajiit's in my opnion.Khajiits are on skyrim just for money,and Redguards hates the cold of skyrim.

Mer and the beast races live a lot longer than humans, they don't need to reproduce as much, designing kids for every race would have been a waste of resources and time.

Also, argonians need hist sap to properly raise their young, and the cold climate of skyrim is probably too harsh for khajiittens.

Orcs has their settlements, made sense with some kids in them, Dumers to are pretty common, most other races is to rare to have many kids, perhaps some Khajiit kids along with the caravans.