The Song "Tea for Two" has been around for a long time. More than 90 years in fact.
It was composed for the Broadway musical No No Nanette, which premiered on Broadway in 1925 after a run in Chicago the previous year (the traditional pre-Broadway shakedown cruise).
"Tea for Two" is a second act song, sung by Tom and Nanette, a couple that quarreled and broke up in Act I, but that has now reconciled. And as you surely know, since anybody who could possibly be reading this knows the lyrics to the song, Tom and Nanette are dreamily contemplating their future.
"We will raise a family
A boy for you a girl for me
Can't you see how happy we would be?
That is how it is often sung, anyway: in the Anita O'Day recording for example.
But, much as I love O'Day, this always pulls me up short. Surely the natural way to hear the second of those lines is for an "AND" to be implied. Nanette is dreaming of having two children with Tom.
So, why "we three"? That only makes sense if one inserts an OR instead of an AND in the second line. Which seems counter-intuitive, given the blissful state Nanette is supposed to be in at the time. Her bliss is qualified by a disinclination to give birth twice?