I occassionally need a friend of mine to pick up my DS from school. (We're talking like once a month.) They would only be traveling a few miles with no highways. My DS is 3 1/2, 33lbs. Would you be comfortable putting him in a booster for that long? I am concerned about her not being able to install my car seat correctly if I left it, and I was thinking that a booster would be easier for her to use. I am just not sure if he is big/old enough to be safe in a booster.