By child I mean one small enough to need a car seat / booster (under 11s or thereabouts).
All safety advice I've ever read clearly states that children are generally much, much safer sat in the back of the car if there were to be an accident.
Passenger seat safety features such as airbags are designed to protect an adult body, and as such may not work well for a young child.
Yet many of the children arriving at my children's school / hobbies travel sat in the front of the car (I notice this mainly for ages 5-8). In some cases it's because the rear seats are occupied with several siblings / lift shares, but in most cases it's not.
If you let your child sit in the front, why?