I suspect the couple of taking class A drugs on a regular basis. They have young children.
Behaviour has changed recently, all indicating drug use. They are known to children's social services for other reasons to do with the neglect of their children.
I don't know if they take drugs. It is through others reports of them that I (and they) suspect they are.
AIBU to report this suspicion to social services, given I don't know for sure?
Preclaimer - I will make it clear that I don't know for sure. And the report would be out of care for the children, no malice towards parents.