yeah, but no.
they would show up with the RN note, materials, and plan...at a minimum. for the note to be written there at the house on the notepad it was on, they either had to be there in the house during the window of time the Rs left for the party, not worrying about when they would return, or sitting up with the flashlights writing it after they were asleep, not worrying about being caught.
...even if they scoped out the place previously, watched them arrive home, had been there waiting...successfully, quietly, navigated the house, got the girl, left the note, thinking it would be easy money....they would slip out as fast as they can with her....if they screwed up while family is right there in the house sleeping, and can't take her for some reason, they aren't going to take the time to stay longer and hide her in a wine cellar they probably didn't know about. they need to leave the body and go....
unless they tied up, knocked out, or incapacitated the family in some way, and are not worried about them at that point. and there's also another child to worry about. that child can also hear things going on....are these guys going to stay and put her down there in that room, in those clothes, with that blanket and her dolls, and leave her there....then still leave the premises undetected just as they came in? if it was that easy to slip in and out, why not take her: dead body or not....and why stay through all that with family simply sleeping upstairs not worried about getting caught?
Even though Leopold and Loeb did kill their victim, and send a RN afterwards, they still kidnapped and took the boy away.