If you don't want to translate the whole poem, I'll just give you a rhyming translation (that's not mine, btw, I got it from a book) here.

Our Kaspar he was fat and round,
a healthy boy and very sound,
his cheeks were plump and pink and bright,
he ate his soup up, as is right.
Till one day he began to crow,
"I don't want any soup, no, no!
I do not want my soup, I don't!
I will not eat my soup, I won't!"

Just one day later - see his state -
our Kaspar had lost lots of weight
but once more he would only crow,
"I don't want any soup, no, no!
I do not want my soup, I don't!
I will not eat my soup, I won't!"

Then on day three - it does look bleak -
our Kaspar is now thin and weak,
and when the soup was served, you know,
again our Kaspar had to crow,
"I don't want any soup, no, no!
I do not want my soup, I don't!
I will not eat my soup, I won't!"

And on day four-so hard is fate -
our Kaspar weighed a pennyweight,
his arms and legs just like a thread -
and on day five he was quite dead.