CHILDS AND CHILDRENS ARE BOTH WRONG
I hear this mistake almost everyday. It is a very common mistake for Spanish people. For example: "My childs get up very early in the morning" or "My childrens don't like pasta".
The mistake happens because Spanish people are thinking about the word "niños" in their head and therefore make this mistake. The rule is that when you are speaking in singular you need to use the word "child" and in plural you need to use "children".
You will say: "Daniel, that is easy". Yes it is easy but I hear the mistake so often that it is worth highlighting it.
Hope that helps!
Soy el director de Daniel Smith + Partners. Tengo más de 10 años de experiencia enseñando inglés a españoles.