A book of Virtue!
You don't have to spend a fortune to give a child a taste of virtual reality. For less than twenty dollars you can get a copy of DK's book "Virtual Reality" which comes with a build-your-own viewer to use with your smartphone, stickers to decorate it, information about the history of virtual reality, and kid-friendly examples to view created by the wizards at Curiscope.
There are VR images of a Tyrannosaurus Rex, a volcano, a space scene, and several more. Interspersed are articles about how VR images are created, displayed, and used.
I am a big fan of Curiscope's work, having previously reviewed their Virtuali-Tee t-shirt that lets you look inside the human body. Notwithstanding that VR has been around since the 1950's, we are still in the early days. This book (and Google Cardboard upon which its viewer is based) are inexpensive ways to get started. Of course, this is not the kind of experience that kids will spend hours at a time immersed in, but that is not necessarily a bad thing. I think it is great that they get a taste of the experience, but there will be time (as the technology improves and their young bodies become mature) to have that deeper experience when they are older. For now, reading a book, constructing a viewer, and having a chance to peer into the future is "just right".