I thought the number of breasts a woman had depended on how many kids she had. Most of the woman in my family had two kids and two breasts, so it made sense. But one of my aunts had three kids. I remember staring at her, trying to figure out where she hid her third breast.
When people mentioned “strip malls” in conversation, I thought the term meant malls with strippers in them. As you can see, I didn’t go out much when I was a kid.
This made me snort audibly.
That could be dangerous, if @WildaBeast’s conclusions are accurate.
As a kid, whenever I heard about some Bill Gates-type who was worth billions of dollars, I assumed they kept those billions in a huge money bin like Scrooge McDuck.
Not to worry, I have plenty of N95 masks left.
When I first heard of a soda fountain, I assumed it was a drinking fountain that soda came out of. Every time I saw a drinking fountain I would go over and see whether it was one of these wonderful soda fountains. My mother noticed and asked what I was doing. After I explained, she told me the sad truth.

So I concluded that sperm floated through the air, more or less like pollen.
Somehow I thought there was a dryer vent duct involved. I told my mother I preferred to get artificially inseminated. I was 10 or 11.
When my dad brought home a cut up tree for cutting up into firewood, I expected him to build me a tree. I was 5 or 6.
At a similar age I believe that the moving tree branches made the wind blow.

And out of wedlock pregnancies must happen when one of your sperm accidentally lands on the wrong woman.
When my mom gave me “the Talk”, she was very vague (and probably embarrassed) and told me that babies were a gift from God. So I couldn’t figure out how those “bad” girls who got pregnant in high school managed to trick God. It’s truly shameful how long it was till I figured it all out. I’m guessing she was of the mindset that if I knew what sex was, I’d go at it. Instead, I spent too many years afraid to even talk to boys, let alone date and go at it…

The recent Veterans Day reminded me that I used to think the Tomb of the Unknown Soldier had the body of the one guy, out of all the millions killed, that they couldn’t identify.
Not an unreasonable assumption given the grammar. We can use the definite article and say “the President” (if you’re in e.g. the USA) or “the Queen” (if you’re in e.g. Canada) because we know that there is only one for the whole country. As a kid, while I don’t specifically recall assuming that the tomb of the unkown soldier of whatever country I first heard had this (the USSR/Russia? the UK? the USA?) had the only unidentified soldier in the whole country/of that country’s entire participation in a specific war, it was clear that he was special.
Now here’s some of my fallacious childhood assumptions:
In early childhood, my Serbian family knew a couple called Dragan and Snežana. The latter name means “Snow White”. At that time, I didn’t know, or better said, it hadn’t occurred to me, that more than one person could bear the same name. Therefore, I assumed that Mrs. Snežana was the Snow White of the story; Mr. Dragan would supposedly then have been the handsome prince.
Around the age of 6 or 7, my father was telling me a “bedtime story”, which was about how humans learned to talk. He said that at first, early humans would “emit sounds” (again, I’m translating from Serbian). For me, audio devices like radios and walkie talkies emitted sounds. Therefore, I imagined a cave man holding a sound box about the size of a transistor radio and listening to unarticulated noises coming out of it. For that matter, I believed that the “Flintstones”, with its depiction of a stone age filled with things taken from modern life, was an at least somewhat accurate depiction of the past. Again about the age of 7, my father had to explain to me that it wasn’t.
On a similar note, when I was about 6, I learned that the composer Johann Sebastian Bach had died following an eye operation. One day, I was watching footage of eye surgery on TV with one or both of my parents. I asked if it was Bach’s eye operation. Although I was aware that Bach lived long ago (I wouldn’t have known the century, but I knew it to be the time when men wore powdered wigs and knee breeches), I wasn’t aware that video technology hadn’t been invented yet, and could thus fathom that this was footage of Bach’s operation!
I used to have the way traffic lights work backwards— I thought drivers took turns stopping at intersections, then going, of their own volition, then the light would turn red or green as a result of the cars stopping or going. It was a real problem when I started driving! Ha, no I was 4 or 5 when I asked my mom while she was driving “how does the light know to turn green when we start to go?”
When I heard people discussing their job’s salary, I thought someone making $15,000 a year would get paid their $15,000 on January first and they’d then need to budget it to last a year.
I think I’ve posted this before, so pardon the repetition.
As a yout I assumed that the music on the local pop radio station was being performed live in the studio each time.
I envisioned the Beatles in there singing “Day Tripper” with the Stones standing by ready to perform “Satisfaction”.
mmm
I thought ‘Do No Pass’ signs on the highway meant don not pass this sign. Couldn’t figure out how any one was supposed to get anywhere, but we where constantly breaking the law.
Babies were in the mommy’s belly, there’s a hole in the mommy’s belly, therefore, babies came out the hole in the mommy’s belly. QED.
When you were old enough and ready to buy a house, you went looking for a plot of land and when you found one you liked, you called The Housebuilders and you told them what you wanted in your house and where you wanted it and they built it to your specifications and you lived happily ever after.

Therefore, I assumed that Mrs. Snežana was the Snow White of the story
Another Christmas thing.
My father’s initials were NOE. We’d get these cards with NOEL on them and I figured they’d been produced to give to my dad – Other families got cards with their husband’s/father’s initials on them.
I did wonder where the L came from.
I thought that even tho people spoke in different languages, they all thought in English.
A few years ago while biking, I saw an gym called “Cross Fit”. I thought it was a gymnasium specifically for Christians. I was not a kid, just an adult a little out of the loop.
I knew that oranges contained vitamin C, that vitamin C prevented scurvy, and that sailors used to get scurvy from lack of vitamin C. Therefore for years I thought they were “naval oranges”, because they had something to do with the navy.
I also thought the gas in a torch was called “profane”, which my dad really liked the time he burned himself on one and said some Bad Words–that time it was a profane torch!
When I was about 4 or 5, I thought that President Lincoln had freed the sleighs which had gotten stuck in the snow. How very helpful of him!
I used to believe that the President was elected because he was the best man in the whole country. So when Kennedy was shot, I couldn’t understand how anyone would want to kill the best man in the country. I was not politically astute at 9.