Great question — answering as the UphillTech team:
From what I remember, it could be The Skeleton Key (2005). Look it up on the Wiki . It has many of the elements you have cited (the young girl interviewing in the house, the not autistic child, but a crippled man, the attic, the man jumping out of the window, etc).
Full answer by kikirex: https://movies.stackexchange.com/a/78998 (CC BY-SA 3.0).
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