I told my cousins minnow were baby trout and was convinced my dad had told me so. He was adamant he never had and I was really annoyed my cousins were right.
I’m in western Canada where we dream about being those fortunate souls who dream about a white Christmas. 
Smart kid!
I thought those giant novelty checks that Publisher’s Clearinghouse showed in their ads were real checks. I thought the winners had to carry that giant check down to the bank to deposit their winnings.
When I was little and would be riding in a car at night I always hoped we would go far enough to catch up to the moon and be directly underneath it. I was always frustrated that we never did.
When my mother got pregnant with my younger brother, and later with my sister, her explanation of how the baby got inside her was “Papa loved mama real close”. After that whenever I saw a man and woman hugging or slow dancing I assumed the woman was going to have a baby soon because of it.
Are you Happy Gilmore?
This has long been one of my favorite quotes, but sadly, it’s not from Twain, whose father died when Twain was 11.
That the stars were only out at night. (Well, if you can’t see 'em…)
This is somewhat opposite of the premise of the thread, but…
Before I had children, I planned to subtly salt their knowledge with bullshit ideas to see what stuck, and for how long. Nothing too serious, just random facts that were completely incorrect.
Since having children, I have done a complete about turn on that. When my son was about 3, I taught him what a coprolite* was. He talked about it for a few days, and then never mentioned it again until a few months ago, when he asked me if a particular (random) stone was a coprolite. He’s almost 5 now, so that word and concept has stuck with him for 60% of his life.
Now, instead of wanting to feed him incorrect “facts” I am far more fascinated with telling him real facts, and seeing what sticks.
- what’s not to love about coprolites for a young boy? They hit the trifecta of fossils, dinosaurs and poo, all of which are fascinating to little boys.
I suggest your co-parent handle teaching the arithmetic.
When I was about six, I accidentally spied a grown man, a friend of the family, when he was peeing and left the bathroom door ajar . From that brief glimpse, I noticed something large hanging down behind his penis. It didn’t look anything like what my nine-year-old brother had, so I decided that it was a second penis that all adult men grew.
This will date me, but I thought Sid Caesar and Imogene Coca were married, and I was disappointed to learn that they weren’t.
I used to wonder who “Pat. Pending” was, why they used a period after their first name and why their name was on so many products.
I watched so many World War II movies on TV with my older brother that whenever I heard an airplane overhead, I was terrified, thinking that the Germans or the Japanese were about to bomb us. It turned out that we lived near a Naval air base.
There was a shampoo called Wash ‘N’ Curl that was advertised on television. It featured women and girls with beautiful curly hair. I begged for a bottle, thinking that it would turn my straight hair curly just like in the TV ads. My 10-year-old self was so disappointed when it didn’t work.
I was further confused about this when I was a kid, because “Professor Pat Pending” (clearly a pun based on “Pat. Pending,” though I didn’t know that at the time) was a character in the 1960s Saturday-morning cartoon Wacky Races.
When my kids were little I’d peel clementines for them. I’d always be careful to remove the skin in one piece for some reason, and I told them if the skin didn’t come off in one piece it meant the clementine was bad and shouldn’t be eaten.
Fast forward 24 years, my daughter for some reason truly believed this and was surprised to learn that it was just a joke.
Woulda been a great opportunity to share this thread with your son:
I saw this poster for “The Santa Clause”:
and thought the character’s transformation into Santa Claus somehow involved having his pelvic region rotated 180 degrees so his butt was in front.