I thought that all languages were actually the same, just our ears differed. So e.g. as a native German speaker, I thought all people ‘speak’ German (I.e. make the sounds of the German language), but the translation of sounds into thoughts by the ears would only work when the source was ‘my version’ of the language. Very hard to put that into words, I just realize…
Another thing was that I had my own religious philosophy. I believed in reincarnation, and thought that all life was just a giant circle where you would be reborn as your own worst victim. Only when you have lived a victimless life, you would ascend into heaven. My go-to example back then was if you stepped onto a worm you will be reborn as a worm that is being stepped on. This one has horrible victim blaming implications when you think about it but in my childlike naivety I thought it was very fair.
Though I wasn’t actually raised religiously, just the prevalence of religion in society led to many of my early theories have religious components.
I thought that between dying and being reborn you spent your time in heaven as an angel. While there, you could select your next parents from all the currently pregnant people on earth. I imagined giant ‘rooms’ full of computers in heaven, where every pregnant woman had a profile you could check out (mind, that was in the early 90s - I like to think I secretly invented social networking^^). Once you decided on a mother, you’d be kicked down into her womb and be reborn. I did realize pretty soon after that this theory doesn’t hold water when you see that many children are not born into happy families, but for a short while I was certain I picked my mother from all the possible mothers around the world. She was very charmed by that :D