Quoting Amber :]:" okay, so turns out my car's latch system only works on the two side seats and not the middle. So I'm ... [snip!] ... it's newer the middle seat's seat belt does go across the chest and does lock when you pull it out all the way and all that."
Seat belt in the middle. I actually do the double thing. My Scion xB only has them on the sides, but I still put my niece's seat in the middle, use the latch system, but I then buckle it as well. It's just an extra precaution 'cause I tend to be kinda paranoid, like "What if the seat belt fails for whatever reason?" Lol.
Fortunately, our new Pilot has latches for every seat in the car, so our little girl will get the latch thing going for her seat.