congratulations, now you have to bought some sweets for your kid(s) for what you saved
InSha Allah you will feel all true happiness in your heart when you will watch kids how they enjoying it
about eye strain, definitely if we used it for a long time and even our children, it will affect on our eyes ( children has more stamina and they can view for more time than us )
about lenses become loose and out of focus of a VR box, it is on our use, some apps have to set manually and some didn't.
i felt out of focus some times in app Sites in VR