Ratios for structured play tend to be 1:8 adults to children (in UK), whilst classrooms are 1:30. Teachers are usually paid more, but not 3½ times more.

NSPCC recommend 1:6 ratio for 4-8 year olds doing activities.

I'd say max 1:3 if you want to give parent level care engaging with a child in activities the child is choosing in a meaningful way.