A finger-trace tickle rhyme: circle a fingertip round the baby's palm or tummy for the first two lines, then walk it up with "one step, two step" before the tickle lands. The anticipation is the whole point, and babies learn to wait for it fast.
A tickle chant: circle the palm, two steps up the arm, tickle under there.
From Mother Goose / Nursery Rhymes (traditional). See the whole collection.
Round and round the garden,
Like a teddy bear;
One step, two step,
Tickle you under there!
About this poem
This is a young rhyme, not an old one. The teddy bear gives it away. Teddies were named after the American president Theodore Roosevelt around 1902, so the words cannot be older than that, and they most likely come from somewhere in the mid-twentieth century. The exact wording shifts from one family to the next. There is no single original text to point to.
This is a lap game, and it works best slowly. The suspense is everything: draw out 'one step, two step' so they know the tickle is coming, then only just arrive. Babies and toddlers love the wait even more than the tickle itself. Expect to be asked for it again straight away.
Traditional rhyme. No printed public-domain source located; wording as commonly recited.