Daydreaming is a beautiful and constructive activity, especially for kids! It is so important to allow and encourage mental downtime and imaginative thinking. Mental downtime, by the way, does not involve screen-related activities. Read on:
"Daydreaming only appears lazy from the outside, but viewed from the inside... a complicated and extremely productive neurological process is taking place. Viewed from the inside, our children are exploring the only space where they truly have autonomy: their own minds."
Check out: https://www.theatlantic.com/education/archive/2013/10/teach-kids-to-daydream/280615/