Headscratchers / Mirai of the Future

• Something about the film always seemed to bug me, but at first I couldn't put my finger on it. Then it hit me: Would a child Kun's age even be able to understand the concept of time travel? In the movie, Kun seems to understand what the past, present, and future are, but I have a hard time believing that a four-year-old is able to understand a concept like time travel. At least, not until they're older. I myself didn't learn about the concept of time travel until I was...maybe ten, eleven, or twelve. So how would Kun be able to figure out what time travel is? Or even think that his parents could be anything but adults?
  • Maybe he watched a lot of movies?
    • Possibly, though kids at that age can understand time, even if it's abstract but, the movie ain't clear if the time travelling scenes are real or just in dreams.