my mother in law does not have an air bag in her front seat (BMW) and wants to take my daughter who is 4 in her booster seat home from school. she would also be bringing home 2 of her school friends in the 2 window seats that have 3 point seat belts. but i told her not to use the middle seat because it only has a lap seat belt. Please can someone advise, am worried i have given her the wrong info