Does this remind you of anything?

Chapter One

Tilly-Tod sounds like the name of just one little girl, but it was actually the name of two little girls who looked so much alike and were so much together that they were almost one, and so everyone called them Tilly-Tod, just like that, in one breath. There was no use in calling one all by herself, because the other one was sure to be close by her and to come running, too.