Although indirectly related to trains was a book (still have but packed away) my dad bought 67 years ago when I was about 7 years old. I think the title was "Fun with Electricity" and cover showed a boy and girl looking at a simple motor. The book discussed batteries, lights, switches, magnets and simple series circuits etc. At the book's end it combined almost everything with building a simple motor. I built that motor and it worked, sorta.
That little book was my start getting a lifelong interest in electricity that led to electronics and engineering. And the train connection (gotta stay on topic!) of course, wiring up my HO (when I was 10 YO), N, O train layouts (after college) and designing signal systems and programming (after retirement).