:smack:
My uncle did a similar thing to me once. He told me that he’d installed this plate on his driveway; whenever somebody stepped on the plate, the garage door would open. He demonstrated it for a while, and I was quite intrigued. It took forever for me to work out that he had put one over me.
Doug Hofstadter talks about an occasion in Italy when he meant to remark on all the little flies (le piccole mosche), but accidentally referred to all the little cows (le piccole mucche) instead. So maybe you were speaking Italian without knowing it 
That is so funny…my dad told us the exact same thing. Must be a dad thing.
We had an uncle who is about 15 years older than us. When he would visit when we were kids, before he’d visit, he’d hit a 7-Eleven and buy some candy. Then when we were out and about, he’d go around the corner and enter his “secret cave” and come out with candy for us. He’d go on about how he had tons of candy and treasure in there. We’d eagerly go running around the corners and spend the next 30 minutes or so trying to find the secret entrance before we gave up. Of course, he had secret entrances all over the area.
My dad always got us on trips…
"hey kids…look up here… it’s what they call the “Great Divide”…
"Really dad?, who discovered it? What’s it for?
“It divides this side from that side”.
or
“Are we there yet?”
“Yeah, but I decided to go somewhere else instead”
Mom got me to try Green Peppers by telling me that they would taste like pickles if you put salt on them…
Isn’t that what they are? 
My dad has my neice and nephews (aged 7-11) convinced that he’s got a big mean cat. The kids are over at the house all the time and they’re constantly trying to get a glimpse of the cat, but the cat’s very private. They’re almost sure there’s no cat, but not quite certain enough.
He also has them convinced that the pool cleaner thing on the bottom, the thing with wheels? Anyway, he calls it “my little man” and says that the little man tells him if anybody pees in the pool. I hope to hell that works.
I forgot about the “little man” in my grandmother’s freezer! He made the ice! This was in the sixties or early seventies before icemakers were very common. I knew of course there wasn’t really any little man … mostly.
Here’s another one I remembered. More of a visual lie. Or a trick.
My niece (5) and I were playing with some small plastic critters. And she insisted that the dog I was playing with goes on the roof. After a few disagreements I picked him up and put him in my mouth. She tried briefly to open my mouth but I wasn’t budging so she turned to her Mom for an appeal. I quickly spit it out and hid it under my leg. When she turned back I visibly swallowed and then opened my mouth to show that it was empty.
She was aghast. It was such a perfect look of shock that I started cracking up. And after a couple seconds the beginnings of tears began and I revealed the dog, safe and sound. She then scolded me “Bad uncle!”
I used to reflect the light off my watch onto the wall and tell my sister that it was a magic ladybug, and if she caught it she would get three wishes.
Kid never wondered why I never tried to catch it.
My oldest son, when he was a toddler, loved to be naked. Every night after bathtime was naked time. Only problem was getting him to get dressed at the end of naked time so I invented the Naked Police.
One day I actually had to call the Naked Police on the phone. I’m not sure if he believed me but when I snuck outside through the back door and pounded on the front door yelling “Naked Police, open the door” he got dressed pretty quick.
I was in the kitchen when one of the geek kids asked what was for dinner. “Fried squid” I told them. They of course went “nuh uh… mom, what’s for dinner?” to which Mrs Geek also replied “fried squid.” They were so convinced that they didn’t believe the chicken was chicken until they actually tasted a bite. The two oldest kids played the exact same joke on Geek Child #3 a couple of years later, so apparently I made an impression.
Mrs Geek was actually quite gullible when we first met (she was 21). The best was when I had her convinced that Germantown MD was populated by Germans, and actually spoke German.
One of my favorites was when we took our neighbor’s teenage daughter and a friend of hers camping. I was actually a bit concerned about fitting our kids, the two of them, and all of our stuff into our minivan. At the time I had a spare clunker car which was my backup in case my clunker truck broke down. Mrs Geek used to call it my Uncle Buck car, and if you’ve ever seen the movie you know what kind of car it was. It was the only car I’ve ever owned that Mrs Geek actually refused to ever get into. I told the two bratty 15 year old teenage girls that they would have to ride in the Uncle Buck car since we ran out of room in the minivan. They, of course, were mortified. You know that mortified expression on the bratty teenage girl in the movie? I got that expression out of both of them. They were so worried about being forced to ride in the Uncle Buck car and if someone might see them that they constantly asked Mrs Geek about it every day for the entire week before the trip. As I’m loading up the minivan, I could hear both of them trying to figure out how low they would have to sink into the seat so that no one could see them through the window, and were quite distressed when I reminded them that they had to sit upright and wear their seatbelts. I had them convinced all the way up until I had to actually get them into the minivan so I could pack stuff around them and close the door.
I used to joke with my late friend that when his son became old enough to talk and ask questions, I would intentionally give him bad information. Me, my friend, and his toddler-age son are in the kitchen, and I say, “For instance, if he ever asks me what a dromedary is, I’ll tell him it’s a turtle.”
The boy looks at us and says, “Isn’t that a camel?”
My friend and I look at each other, dumbstruck.
“Did you teach him that?”
“-I- didn’t teach him that!”
The boy just grinned at us.
This from a reader’s letter in the Times a few day’s ago.
My father used to tell us that when the ice-cream van sounds its chimes it’s signalling that it’s sold-out of ice-cream.
I remember a story where my grandparents couldn’t afford the ice cream truck when my aunt was little, so they told her it was the Music Man, and he just drove around playing music for all the kids. According to them, that theory lasted a good long while.
A friend of mine is a giant of a man. 6’6" or so, easily. And built like a mountain. Once he was in a public restroom when a little kid said, in awe, “Wow… you’re TALL.”
And Casey, bless him, said, matter-of-factly, “That’s because I ate all my vegetables when I was a little boy.” From one of the stalls came a delighted “See?! I TOLD you!”
I remember reading this story in an issue of Reader’s Digest once:
A phone operator (you know, the people you used to get when you dialed 411 or 555-xxxx) once got a call that went, “Hello, Disneyland? This is the Smiths. We’re NOT COMING!” sounds of children wailing in the background click
When my sister was little, and she’d misbehave, either one of my parents or I would pretend to call “Santa” or the “Easter Bunny” and tell them she was was bad and shouldn’t get any presents and/or candy.
Aha–I found it!
We’re friends with a couple that has four children. The mom is a nurse. Her sister is also a nurse but she works in Guam, where she makes very good money. The kids are aware of this. Last April Fool’s Day they sat the kids down and explained to them that they were all moving to Guam for a year, to live in a hut with no electricity (and therefore no TV or Playstation), so Mommy can make a lot more money working as a nurse. They kept it up just long enough to get the kids to *almost * start crying, then said “Ha, April Fool!”
I think I’ve posted about this before, but when my younger sister was little, I told her The Beatles’ “Eight Days a Week” was a reference to the British week, which has eight days due to the metric system. 
I was watching an old black and white movie a few years ago. My son came down stairs and asked why everyone was wearing black and white. I explained that it was the law and everyone had to Then while I was explaining about the color police coming after you if you wore colors ,my wife overheard and stopped me when I was on a roll.