Q: I wanted to know, what is the correct Sunnah way to address your Mum and Dad? What did Nabi (Sallallahu Alaihi Wasallam’s) blessed children address him and Sayyidina Khadijah (Radiyallahu Anha) by? Was it Abba and Amma? Or Abu and Ummi? Or any other titles?
A: Words of respect are closest to the sunnah.
We have not come across this. The etiquette is that both the parents must be addressed with words of respect.
And Allah Ta’ala (الله تعالى) knows best.