Hey ScientiaOmnisEst
I feel like the whole problem lies within the last sentence that you wrote... namely, the problem Scientia is not about that you gave up your fantasy-thinking late in your age, as you say, but the problem is that you "see this as a problem", & that you have "fear & anxiety" towards this thing!
Reading your whole post, I didn't undertsnad what's the problem, what's wrong if you give up fantasies late in age! Actually, what's wrong at all if I keep believing in fantasies (e.g. Santa Claus) for my whole life?!
I mean fantasy-believing & wild imagination is a very beautiful thing, & actually it's a unique kind of intellect & genius, not just in children, but also in adults who have them. I mean where do you think that famous genius fantasy novel writers such as J. K. Rawling, J. R. R. Tolkien, or (my hero) Stephen King got their genius fantastical novel ideas from?! I remember reading SK saying that he still believes that there's a mysterious metaphysical existence that is there lurking in the shadows beyond our limited-perception of reality
And to tell you even more, if you read in science, especially the philosohpy of science, cosmology, & quantum physics, you'll find that even science admits that our minds have a limited ability of perception of our surroundings, & the universe, that science still lacks behind in finding out the mysteries of many yet unsolved questions, like human conscience, the existence of God, or how did the Bing Bang happen...
So, yeah, perhaps I agree with your mom

believing in fantasies is a good imagination exercise of the mind, & its unique human characteristics that are not possessed by lower beings (e.g. animals)...
I don't undertsnad why you should have any fears about this beautiful thing