I'm assuming if your son is a pre-schooler that he's less than 4 years old. Even if he meets the minimum 40lbs for boostering, kids his age are not booster ready. Most kids are ready for boosters around 5 or 6 years old. If your son is younger than that he should probably be riding in a 5pt harness and not a booster, especially in the front seat even with airbags off.