I think it's more rare here than you would guess from our media and fictional accounts. When I was a kid I think I only met one kid with an imaginary friend, so the article's statement that "If you didn’t, chances are you know someone who did" was true in my case. On the other hand, it did seem really weird and notable to me at the time. In contrast, lots of kids in stories and on TV and in movies had imaginary friends. In the 1980s it freaked out American parents, too, and they worried about their kid being unable to tell the difference between fantasy and reality, and it became a huge media and cultural thing to talk about how it was okay and not something unhealthy, like "cross-dressing" more recently. I think in the service of that, it was not surprising for a kid in a story to have an imaginary friend. To me, it was something that was normal in a story but not in real life, like when a character in a story got to fly in an airplane.