[No2much3]

If they were getting high at home with kids, of course if they were watching the kids then Children's Services would need to remove the kids from the home as an unsafe environment.

I have to assume you also include those dads who spend Sundays watch football on TV and drinking a six-pack of beer. They are drunk and not able to legally operate a car, but is it ok for them to have custody of their children?

Where is the difference?

[A CA Guy]

The difference is that if they lack capacity and they can't handle a medical emergency with their kids because they are drunk, they could still lose the kids by endangering their lives with their drug use or drunkenness.