Perhaps you could use this one I wrote for my daughter:

Not far from here (about a mile)
There lives a hungry crocodile
Who lies in wait throughout the day
For children who might pass his way.

And when one does, despite the laws,
He grabs them in his greedy jaws.
it doesn't matter if they squeal!
It doesn't put him off his meal.

He thinks that children are delicious,
Much tastier than ducks or fishes,
And though one seldom passes by
He's always watching with one eye.

A week ago, my little daughter
Went walking by the pool of water
Where Crocodile quite hidden lay.
He though, "This is my lucky day!"

He swished his tail- the water splashed-
And through the undergrowth he crashed-
Then Alison let out a wail-
He'd caught her by the pony tail!

But, luckily, she'd in her hand
a little silver magic wand
Made for her by her Uncle Rick.
Her frantic waving did the trick-

A BOOM! a FLASH! the lightning flared
And back into the water hared
The crocodile, now quite defeated-
His size to inches was depleted!

So Alison is safe with Mummy
Instead of in a reptile's tummy.
And as for Croc? I'm sad to say
The spell wore off just yesterday.

So now his size is back to normal,
He's ravenous, and his temper's awful.
So, Children, don't go near his pond
(unless you have a magic wand).