I'll be mom

I would like to know the origin (and time of creation etc) of the phrase "I'll be mom"/"I'll be mum" in relation to serving tea.

The earliest citation the Oxford English Dictionary gives for the phrase "to be mother" in the sense "serve out food or drink" is 1926, in one of Shaw's plays. The earliest one specifically relating to tea dates from 1934: "‘Shall I be mother?’, said Ella, and started to pour out the tea." (VSD)