Applications of New Code and Supervision 4

 Your responseResponse example
How is this an ethical problem for the supervisor?

this is outside of the realm of his his job.

The RBT is not keeping to the boundaries of the behavior therapist role, which can cause serious ethical problems especially if it is when he is billing for services. The supervisor is accountable for his actions (Standard 4.04).
How should the supervisor go about setting new boundaries?

Shut it down.

Begin by talking to the RBT and providing concrete rules for talking to families

Approach the parent of the family who is most involved with his diet advice and explain the situation.

Continuing with the advice after work hours is an option, but it will create a multiple relationship and should be avoided (or alternatively, the RBT can be switched to a different client)