Bruce Springsteen recorded a simpler version with some traditional lyrics plus a few he made up himself on his CD HUMAN TOUCH. Apparently his grandma used to sing it to him too and when he first started having kids, it came back to him.

His version is short, sweet, and simple with no sexual ovetones. Just a nice little lullabye. He adds a verse about sleeping beneath the starry sky just in case the kid you're singing to doesn't get the hint and start yawning. His wife sings a nice harmony with him. Check it out.

His version is a little simpler than the melody I recall but no less sublime:

PONY BOY
Traditional
arrangement and added lyrics by Bruce Springsteen
Copyright 1992 Bruce Springsteen

CHORUS:

Pony Boy, Pony Boy
Won't you be my Pony Boy
Giddy-up giddy-up giddy-up Whoa
My Pony Boy

Verses:

Ride with me, ride with me
won't you take a ride with me
underneath the starry sky
My Pony Boy

O're the hills and through the trees
we'll go riding you and me
giddy-up giddy-up giddy-away
My Pony Boy

Down into the valley deep
'neath the eaves we will sleep
sky of dreams up above
My Pony Boy

You can sing the Chorus between each verse or whenever you want. He adds a nice little instrumental bridge before the final verse and chorus. It's quite sweet.