I've always put my son in the window seat. Firstly, because he was in a car seat and had to be placed there. Since he aged out of the car seat he still goes next to the window because he loves watching everything out there, especially as we come in to land in a new city he's never seen before.

I would thing twice about using the CARES instead of the car seat. The safety seat raises the 2 y.o. up high enough to see out the window, which was a real benefit until my son got tall enough to see out just sitting in the seat.

Personally I think "stranger danger" is greatly exaggerated and I would not worry about my child sitting next to an unknown person if I was present, at least not in terms of his safety. I would monitor his manners to make sure he didn't bother the person, but the risk of that person being a child molester is too small for me to think about.

However I wouldn't put a 6 y.o. in the aisle for safety reasons, but that's because he'd be likely to get banged/bashed/slammed into by beverage carts, carry-ons, etc. My last few flights in aisle seats I ended up with bruises from people who couldn't walk down the aisle without swinging their gear all over. [and when will airlines impose their carry-on restrictions?! ]