I went Googling for "nelly in the belly"—also "nellie in the belly"—and found the following variations.
(None of the sites where I found these quotes cited any sources.):


Oh, the cow kicked Nellie in the belly in the barn.
The Doctor said it wouldn't do her any harm.

The cow kicked Nellie in the belly last night,
And the doctor said she'd be alright.

The cow kicked Nellie in the belly in the barn,
And one more drink won't do us no harm.

Who hit Nellie in the belly with the jelly
And put her in hell of a jam?

You don't kick Nellie in the belly in the barn.
The poor old cow ain't done any harm.

Who hit Nelly in the belly with a flounder?
Who's gonna answer to her mom and dad?
Nelly says her belly's stinky smelly from that fish.
Grandpa claims it's all too brisk.
So who hit Nelly in the belly with a flounder
Down at the dock in Wildwood Bay?
That kid should be careful next time,
Catching that fish, swinging that line,
Cos Nelly's little belly might be in the way.

*

There might be more out there; I got tired of looking.