It sure was, and possibly a subconscious "cry for help" from Patsy.
Not to mention that the "ransome note" was left right on the landing of the stairs that led to their bedroom. That would be one brave intruder; he takes the little girl from her room, carries her down to the basement and kills her, then takes half an hour to write the ransome note that demands exactly the amount of Mr. Ramsey's bonus, walks upstairs and plants the note on the landing...he must be able to walk on air, as well.