K-I-S-S-I-N-G

From my memory:

—— and —— (* Names a boy and girl *)
Sitting in a tree.
K-I-S-S-I-N-G.
First comes love,
Then comes marriage,
The comes the baby
with the baby carriage.

Some small differences…

Source: Eskimo

—— and —— (* Names a boy and girl *)
Sitting in a tree.
K-I-S-S-I-N-G.
First comes love,
Then comes marriage,
Then comes (another kids names)
With a baby carriage.

Oh look at this. I found another verse.

Source: Mama Lisa

(Girl’s name) and (boy’s name) sitting in the tree
K-i-s-s-i-n-g! (spell it out)
First comes love.
Then comes marriage.
Then comes baby in the baby carriage,
Sucking his thumb,
Wetting his pants,
Doing the hula, hula dance!