Assuming things still exist for one or two seconds after losing sight of them isn't a difficult task. It's still a pretty basic momentum calculation. It's not about modeling the mind of the child to know if they'll continue: the dumbest option says motion will continue and gives you the safe result here.

> Why do you think so many animals, with such great perception, end up road kill?

Because they're not cautious around cars and/or wait for the last second on purpose? Switching to the perception of the thing getting hit is a very different context.