M.B.
I have a Honda Pilot (2007) model and travel with my grandchildren a 3 year old in a car seat and 11 year old. Car seat fits well in middle, side or in 3rd row when needed. I work with Teen mom's and through the meetings I have learned that the middle is always the safest for the baby if only one..otherwise you do what you have to do...I will tell you that putting the new baby in the middle next to the older child can cause issues...
Good luck! I also had a highlander and loved it... the Pilot is a little roomier.