After teaching English for almost a year to native Spanish speaking students, I find 90% of the time the students make the mistake of saying, childrens to pluralize more than one child. This word DOES NOT exist within the English language.
If you want to say more than one child YOU SAY: Children
If you want to say just one child only, YOU SAY: Child
Children = more than one child; already plural
Child = only one child; for singular
Other typical example we have to be careful is mouse:mouses, foot:foots, etc.
That is true, it could be because in Spanish, all (or almost all) the plural is formed by adding the 's' at the end of the nouns. So, the singular is 'niño' (for child) and the plural form is 'niños' (children). While we are learning that, the 's also contributes for the confusion, for example: men's.