Hi,
An alternative spelling is ittsy-bittsy.
There's also teensy-weensy (derived from 'tiny', I imagine). An adult might occasionally try to be cute by saying to a friend:
A: Would you like some more cake?
B: Oh, just a teeny piece, please.
There was a pop song many years ago:
She wore an ittsy-bittsy, teeny-weeny
Yellow polka dot bikini
Just a teeny comment, Clive