I just learned to pretend like it didn't worry me and say "well, he's hardly going to coming in to sleep next to me when he's 15!" or "I'm sure he'll sleep beautifully when I need to start getting him up early to go to school!"

I found that once I started going into detail about what was going on I got the unwanted advice which I suppose is fair enough...people generally do want to help (or feel superior because they think they know everything and their methods are the best ) so best not to engage in the discussion in the first place.