I'm not a kid anymore, but I've played Pokémon games actively for 10 years or so and I still can't remember some type weaknesses! It's starting to be a little frustrating and it seems that I'll never learn them all. When playing at home, I usually end up asking questions like "Is Steel super effective to Poison?" and my boyfriend answers, good thing that he remembers them correctly. But I'm always like: "Is rock super effective to ice? No? Why wasn't this fighting attack super effective with this Pokémon? Ghost and poison? No idea!". I do remember usual weaknesses, like Fire-Grass or Psychic-Fighting but when it comes a little more rare type matchups, I'm at lost. Like Fighting and Poison? I actually started to wonder that when I wrote that down, and I seriously have no idea. Well, I only play in-game which is good for me because in competitive battling I would be an easy catch to anyone.
//Have to add this story I heard once. I read this from another Pokémon forum years ago, but there was someone who couldn't figure out how to get out from Viridian Forest in FR/LG. So she/he just walked around the forest and levelled his/her Bulbasaur up to Venusaur until he/she finally found a way out from the forest. True, the forest might be a bit puzzling and labyrinth-like but I don't think it's not that difficult really.