3 through 15

Tess hasn't really had a normal childhood according to her best friend Jenni. She has never been trick-or-treating or to a sleepover and shes never dressed up in the disney princess outfits ethier. So Jenni advises a plan to re-live Tess's life over again starting at age 3 and going all the way up to age 15. What will happen at a party that they will go to that will be a life changing expirence? What will happen throughout the journey of being a kid again?