well I have 2 kids and have them on either side of the car. My minivan has bucket sets in the middle row and a full seat in the back, but neither car seat fits in the middle. The only vehicle we had that the carseat would fit in the middle was our jeep grand cherokee. Now both of my kids sit on the sides of the car, as they don't fit in the middle.
I think you may have gotten the idea that the middle is not the safest, was because if they are on the sides your front seats protect them from going anywhere, if in the middle there is nothing protecting them, but if they are on the sides, then if you get side swiped, it affects them that way. I think it is a matter of where you want them, and/or where they fit. good luck