My kids also enjoyed checking out my miniatures and RPG books. My son could flip through my various monster manuals for hours. So when they were little, I let them play with my boardgames and books. Nothing systematic, just playing around.
At 7 or 8 we started playing
Talisman. It's not the greatest boardgame design by modern standards, but it's pretty fun for kids. I has the minis and the RPG-like monsters, events, and progression. We played a shortened version where you need viewer trophies to level up.
By about 10 they were interested in actually playing an RPG, so we played
Beyond the Wall, an introductory old-school RPG aimed at adolescents. It's easy to get into and a lot of fun. Highly recommended.