Is childrens a regular noun

No, the plural form 'children' is an irregular pluralnoun (there is NO 's' at the end of the Word).

A regular plural noun is a Word that is made plural by adding an 's' or an 'es' to the end of the Word.

An irregular plural is a Word that is made plural in some other way.

The Word 'children' is the plural for for the singular noun 'child'. The plural is formed by adding 'ren' to the end of the Word (not 's' or 'es'); a irregular plural form.