I've got four children and expecting another in October. When baby arrives one of my children will have to sit either in the middle seat of my middle row with a lap belt only, or in the front seat of the car with an air bag. Which is safest? Oldest child is 9 years old and about 140cm. She's happy to use a booster seat still or can go without if it makes a difference. Would be grateful for any advice as don't really want to buy a new car!