Kids think others see like they do. They won’t know their vision is blurry because they don’t compare their vision to others.
Over the years I have examined many kids with “no vision problems” who really couldn’t see well. I have seen parents berate themselves, even break out in tears, for not realizing their child had a vision problem.
I recommend every child have an exam by 5 years old and then every year after that. Sure, many kids don’t have vision problems, but don’t you want to be sure?