Who's sitting on the hill with Jack?

JILL.

Of course, Jill is the white bird sitting on the hill with Jack :-) !

The next two lines of the verse are:

Fly away, Jack. Fly away, Jill.

Come back, Jack. Come back, Jill.

Grampa John plays this "finger trick" game with little children the same way he used to play it with the college students he taught.  I wonder how many of you readers know the game.