Little Tommy Tucker is an old nursery rhyme first documented in 1744. Little is known about who Tommy Tucker but the name might be a blanket name given to any orphan.
In some versions of the song the bread is white instead of brown. In that case the meaning would be more ironic as white bread (and butter) was out of reach for people of lower classes in the 17th and 18th centuries.
A version of the song published in 1899 in “A History of Nursery Rhymes” was slightly different:
Little Tommy Tupper,
Waiting for his supper,
What must he have?
Some brown bread and butter.
“Little Tommy Tucker” Lyrics
Little Tommy Tucker
Sings for his supper.
What shall we give him?
Brown bread and butter.
How shall he cut it
Without a knife?
How will he be married
Without a wife?