In class writing (Pobby and Dingan)

In the world, some groups of people have their imaginary friends when they were young. Also in the book pobby and dingan, the narratter Ashmol's sister, Kellyanne has two imaginary friends. Their name are Pobby and Dingan. I think they are not real people, because Ashmol never see them once. Also there is a evidence from the book shows Ashmol do not believe pobby and dingan are real, "'Pobby and Dingan aren’t dead,' I said, hiding my anger in a swig from my can of Mello Yello. 'They never existed. Things that never existed can’t be dead. Right?" Also Pobby and Dingan never answer or talk in the book, either. The most confusing thing for me is why the whole family believe Pobby and Dingan are real people. However I still think Pobby and Dingan are just imaginary people not real people who lives in the real world.