"The mother wants to see the children."
Translation:La madre quiere ver a los niños.
Hijos are always the children "of somebody". It wouldn't really fit in this sentence if you don't specify whose children they are.
I think los hijos should be a correct option. What would the distinction between los ninos v los hijos?
The sentence implies they are HER children --- therefore "hijos." At the very least it is ambiguous and should accept either.