Getting the number of children and grandchildren

How would I go about getting the number of children pages under a parent page (not including grandchildren) and displaying it? I would also like to get the number of grandchildren and be able to display it separately…

For example, I’m trying to display something like:

There are 56 [child] games with 93 [grandchild] expansions.

on the parent page.

The parent page is games, the child is game name, the grandchild is expansion name.