I think by the time they're nine or 10 years old, they can be champions. I don't think a three-and-a-half-year-old or a four-year-old who doesn't attach their own belt in their own vehicle with the mom there is going to be able to do it in a bus. Manually, their dexterity is not there, which then requires another adult to actually do that work for them.
On April 4th, 2019. See this statement in context.