This was someone who told on you to your mom or dad. We had a Tell-Tale-Tit in South Durham, where I was born. But not a Telly-Pie, sadly. Never heard this beautifully sadistic rhyme, sang by kids to other kids. It's from the late nineteenth, early twentieth century:

"Tellypie-tit,
yor tongue shall be slit,
an' aall the bairns i' wor street
shall hev a little bit"

(Tellypie-tit,
Your tongue shall be slit
And all the kids in our street
Shall have a little bit.)

Nobody likes a grass, kids!