A catastrophic loss of aircraft is not something most seat belts will get you through. You should also know that one of the biggest risk of plane flight is getting you head or child's head slammed into the ceiling during turbulence. That is why the seat belt light comes on at the first sign of unstable air. Just like a child in the backseat of a car that cannot immediately care for themselves they should be strapped in all the time. If you do not buckle or unbuckle the child depending on the conditions in a car why ever unbuckle them on a plane. The wisest flyers are judicious at keeping strapped in on any plane.