People have the common idea thar pokemon is childish mainly due to Nintendo's means of marketing it. Also, R/B were terrible games graphically according to many reviews of it I've read at gamefaqs.com. many people tend to listen to these "experts" and take on their opinion because they are too stupid or lazy otherwise to have their own opinion.
It is true that the average person may play pokemon games and see a childishly easy RPG that really falls short of a true RPG (like FF or Kingdom Hearts), but many people like us, play a pokemon game and see a unique game that offers greatly customizeable gameplay. Some are attracted to the battling aspect while some are attracted to the collecting aspect, but we all view the pokemon games as great, underrated games.
It is true that the average person may watch the pokemon anime and see a childishly repetitive plot, but many other people like us, watch the pokemon anime and are treated to a vast fantasty world with great characters and vividly rendered pokemon.
I may not be the most open about my fandom, but a lot of my friends know it anyways, along with every other major video game series that i'm a fan of. I usually take my Game Boy equipped with a pokemon game on test days so that I can entertain myself when I'm done and waiting for everyone else to finish. I usually pack my Game Boy with me when I go out by myself to pass the time between tasks. Sure i may get wierd looks from fellow students or strangers passing me by on the sidewalk, but I couldn't care less (it does really annoy me when little kids walk up to me acting like they are pokemon experts and then ask me the most n00bish pokemon questions when I prove them wrong. XD)