From Muppet Wiki

Nanny is the kindly woman who takes care of the nursery on Muppet Babies. She's always seen from the babies' perspective, so the audience never sees her face. The most frequent view of her is her legs, clad in green and white striped socks beneath a pink skirt, and her purple shoes, entering the room. However, her full body was also displayed, including her arms and her purple sweater, but always cut off at the shoulders or otherwise obscured.

Nanny's existence is not limited to the animated Muppet Babies world. A framed embroidery of her can be seen decorating the wall of Baby Piggy, Baby Fozzie and Baby Gonzo as Wee Willie Winkie (in the guise of Baby Kermit) peers into their window in Muppet Babies' Classic Nursery Rhymes.