Monsters on my Shelf
(skip counting by 3)

Monsters, Monsters,
Come to scare me,
Some are bald,

Some are hairy!!!

There's not one!

There's not two!!

Come in threes,

What they do!!!
3, then 6,
Then 9, then 12,
15 monsters on a shelf!  
Start with three,

Then six,
/
Then nine,
//
Monsters scare you,
Every time!
Now there's twelve,
///
Now fifteen,
////
Can't you see there's two between...
3 and 6, and 9, and 12,
15 monsters on the shelf!
////