Saying Wanda’s children are real simply because she created them is like saying that the hologram in Lanterns is real simply because John can create it. The ability to create something doesn’t automatically make it a real living thing.
I think it’s time we finally admit it: Wanda’s children weren’t EVER real. Vision himself confirms this within the first five minutes of VisionQuest, saying that “Wanda created a new life with a family that wasn’t real.” At this point, it’s hard to argue otherwise.