Ruling on teaching the second wife’s children on the first wife’s day

What is the ruling on going to the second wife on the first wife’s day in order to teach the second wife’s children, during the day when they come back from school?

Praise be to Allah, and blessings and peace be upon the Messenger of Allah:

We put this question to Shaykh Muhammad ibn Saalih al-‘Uthaymeen, may Allaah preserve him, who answered as follows:

“This is not allowed, it is haraam.”

Question:

But the children need to be taught.

Answer:

“He should bring them to the house of the wife whose day it is. And Allaah knows best.”