There is no such word as womens. Ever.
One adult human female is woman. If she possesses anything, it's the woman's item.
More than one is women. If they possess anything, or if anything is designated to their exclusive use, it's women's.
Women's Room. Women's Wear Department. Women's fashions. Women's hairstyles.
It's fair, really, because it's exactly the SAME rule for men:
Men's Room, Men's Wear Department. etc.
And children, too.
One is a child. It's a child's toy, if there is only one child attached to it.
More are children. It's the children's toy if there are more than one child owning it.