You can't do this out of the box. There's no easy way to check all child records on a parent record and then close the parent record. You'll either have to find another approach, or do some custom development to create a workflow that can do
what you want.
I'd start looking here: https://msdn.microsoft.com/en-us/library/gg309745.aspx?f=255&MSPPError=-2147217396
The postings on this site are solely my own and do not represent or constitute Hitachi Solutions' positions, views, strategies or opinions.