DS9 was/is very much like this. Parasaurolophus was his favorite for years and he was always mad that it wasn't one of the popular ones for shirts and toys.
Google saved me. Once he started reading that also helped a LOT. His need for precision and knowing EVERYTHING is pretty much endless. The most memorable one for me was his absolute NEED to know EVERYTHING about where babies come from. We managed to keep it sort of vague until 4 or 5 and then gave in to the relentless questioning and covered pretty much everything. Even then he still wasn't completely satisfied when we refused to "show me!" lol
