Is it kids' playground or kid's playground?
It would be a kids' playground. There will be more than one kid
on the playground, so there are kids. Then to make that plural, you
would have to ad only an apostrophe and not apostrophe then an "s".
Where as if there were only one kid on the playground then it would
be a kid's playground, because there would only be one object
there.
Hope this helped.