Plot hole: According to the family tree viewed in this episode, Penny "Grams" Halliwell was born on 6/23/1937, and her daughter Patty, the Charmed Ones' mother, was born on 4/5/1950. In addition, Patty's father was born in 1930. So, according to this, Penny gave birth to her daughter at age 12, while married to a 20 year old man. That's quite outlandish, to say the least.
Plot hole: When teenage Prue has run away with the demon, and Phoebe and Piper find her in the park, teenage Prue is 'killed'. Her sisters drive her home to get Leo to heal her, but shouldn't they have just been able to call to Leo to orb to them when Prue was first hurt, and heal her in the park, and save driving back to the Manor and risk Prue dying?
Plot hole: In this episode the Charmed ones state that the ghost can only be vanquished by a potion on the ghost's bones (grave) or if the haunted object is destroyed. But in episode 1-20, "The Power of Two", Prue has to die herself to be able to vanquish the ghost with a spell, and we learn then that this is the only way to vanquish ghosts.