The safest place for children in the car is always in the back seat behind the passenger. This way, when you and your child get in and out of the car you are on the safe side of the sidewalk away from moving traffic. The space in the middle is ideal, ONLY if a three-point belt is available here. But it usually is just lap belts.
Driving on the passenger seat is generally permitted for children up to 12 years or 150 cm of height if driving in an appropriate child seat. However, please read the instructions manual from your cars manufacturer carefully. You will find important information, particularly for the use of child seats in combination with airbags.