Enable Parental Controls but allow Google Drive and game playing
Not a complete answer but might help someone else looking for a solution for Steam. 

I had no end of trouble if Steam was installed in /Applications, even if there was no restrictions on which applications could be run. 

However, if Steam was installed in the user's Desktop (or somwhere else in their home directory) then after initial approvals on first run it ran without subsequent parental invovement. I had no restrictions on executing applications, I suspect it may have different had there been any restrictions in place.