Here are the lyrics my Dad used to sing:

When the fire burns low on the great big stove
And the house upstairs is still,
Momma sings me a dear little sleepy song
Of sheep that go over the hill.
One steps over and one comes next
And one comes after behind.
The gray one's nose to the white one's tail,
To the top of the hill they climb

My son just revived it to sing to his daughter.
fsc