no seat is safest then the other. I would keep your 3 year right were he is and put infant in middle of possible so that someone can sit back there when needed.

say up to you ..yes hey say middle but I never did and have bucket seats (harder to get baby seat out of middle) which I'm sure is why they say safest. They don't recommend the baby mirrors on the seat but if you have one then I'd say infant behind passenger so you can see into mirror from rear view mirror! @katie86

I've heard you put the most vulnerable baby in the middle. which I would assume is your 3 year old being as his carseat is more open than a newborns.. if his carseat doesn't fit in the middle, then the newborn would go there.

My son is behind the driver because that's the next safest place besides the middle. My daughter is ginormous for 4 and her car seat is way too big so Zayd's carseat didn't fit in the middle properly which was even more of a safety hazard than just placing him safely on the side

Even though you can place them on any side the safest spot for an infant seat is in the middle. @kenitra

The newborn/infant seat goes in the middle spot.