Continuity mistake: After Marnie and Dylan get out of the cab and walk up to the first building, they're not carrying the luggage, then in the next scene, they have the luggage again.
Continuity mistake: When Aggie and Marnie are walking when they first get to Halloweentown, the grandma's arm goes from being locked into Marnie's arm to being free, to being locked in with Marnie's arm again.