children's or childrens'

[Unregistered]

I am a little confused whether I should use childrens' or children's in something I am writing. The context is a wall, filled with childrens'/children's pictures - these are pictures that were drawn by children(not of children) and so collectively the pictures belong to may different children.

Any help much appreciated.

 

[Linguist__]

(Not a teacher)

Children's.

I don't think 'childrens'' exists as there is no such word as childrens, and you only put the apostrophe after the 's' when there is already an 's' there.