sian, west wales, I am well along in years, but my memory is pretty good for some things, not completely Alzhammered! I would guess WW1 as well. As kids I am sure that we sang verses in the 1930s.
The hymn itself was often heard in the Depression days of the 30s. There was a soup kitchen variant which I vaguely remember. Our parents would not let us go to the parts of town where the Okies could be found on the move, detoured around the town center by police. We were warned away with stories about these people, but that only encouraged some of the bravest, so we saw a little of them.

There were worms, worms, worms in the bread,
In the bread, in the bread,
There were worms, worms, worms in the bread
Where they fed us (on the street ?).
I can't remember any more.