I have very strong views on lying to kids: I think you both should and shouldn't do it. "Lying" covers a range, including saying things that hurt your kids and your relationship with them, and others that help them grow into an appropriately skeptical adult. The distinction is whether I'm leaving them believing something false.

For example, if my kids were asking for ice cream and I thought they'd already had too much sugar, I might be tempted to say "sorry, we're out of ice cream." Or if there's an ice cream truck and I think it's overpriced I might be tempted to say "sorry, I don't have any cash on me." But I'm not willing to say something false with the goal of causing them to believe something false. [1] In addition to that just being wrong:

• It's important that the kids know that I'm fundamentally on their side, and lying for my convenience would burn trust when they'd eventually figure it out.

• Kids are building a model of what is and is not ok, and "out of ice cream" and "no cash" lead them in the wrong direction.

Instead I would say "sorry, you already had candy" or "the ice cream costs more than I'm willing to pay" (which opens the door for them to offer to spend their allowance). Maybe they fuss, but they generally don't: I try hard to be predictable so this won't be much of a surprise to them, and they know I won't give in to extended fussing.

On the other hand, some false things I might say [2] about ice cream:

• "Ice cream is actually cold mashed potatoes"
• "We should eat ice cream for every meal"
• "I'm going to put your ice cream in the microwave"
• "When you're done with your ice cream, put it down your sister's back"

In all of these I'm saying a thing I think is false, but, very importantly, I'm not going to let the conversation end with them believing something false. Either they will realize it's false immediately, or I'll need to accept that my playfulness was miscalibrated to their perception and disclose the lie.

This builds the skill of thinking about whether things you hear are true. If I only ever said true things to them we wouldn't be able to practice that. This does need to be matched to their ability: a very little kid will push back on "you're made out of ice cream, and I'm going to eat you up!" but not "we can leave the ice cream out as long as we want, it won't melt."

It also functions as a good jumping off point. If I suggest they pour their ice cream on the floor when they're done with it, that lets me reinforce or explain good behavior. This could go different ways with different kids, with age being a large component. Thinking about how this might have gone with my kids:

Age 7:

Me: When you finish your ice cream, remember to pour it all over the floor!
7yo: That would make a mess. Leftover ice cream goes in the sink.

Age 5 [3]:

Me: When you finish your ice cream, remember to pour it all over the floor!
5yo: That's silly! It goes in the trash.
Me: Actually, leftover ice cream goes in the sink. It's going to melt, and get all liquidy, and liquids go in the sink.

Age 3:

Me: When you finish your ice cream, remember to pour it all over the floor!
3yo: No!
Me: Why not?
3yo: Food doesn't go on the floor!
Me: Where does it go?
3yo: I don't know.
Me: You give it to me, and I put it in the sink.

Age 2:

Me: When you finish your ice cream, remember to pour it all over the floor!
2yo: Ok! [immediately pours ice cream on the floor before I can clarify that this was a joke]

Which does illustrate something important: you really do need to be a good judge of the kid you're interacting with. These depend on the kid knowing the actual rule well enough that you can play with it. I only want to say "let's juggle ice cream" to a kid who knows enough not to try, but if they do know then me being silly about it reinforces the "don't juggle ice cream" norm and signals that I trust them enough to know they wouldn't do it.

The final reason I say false things to kids is just that papa trolling is fun for both of us, as long as I don't do it too much. [4]

It is a bit weird to be both very strongly opposed to lying to kids and also say false things to them many times a day, but "am I leaving them with a false view" cleanly separates the harmful and beneficial cases.

[1] This means we don't tell the kids that Santa or the Tooth Fairy exist. But we do explain the overall situation, with how for some families it's a game the parents play with their kids, so that we don't have our kids going around spoiling it for other families.

[2] The first draft of this post had "everyone can have ice cream except Nora" but then I checked with her and it wasn't clear she would have understood it to be joking about unfairness. Then I asked her about "when you're done with your ice cream, put it down your sister's back" and she got it right away.

[3] After writing this post I tried it with Nora, age 5.4:

Me: Nora, I wanted to check that you know something. When you're finished with ice cream, it's important to pour it all over the floor.
Nora: No! [laughs]
Me: Why not?
Nora: Because then you and me and Mama would need to clean it all up!
Me: What should we do instead?
Nora: Just leave it alone.
Me: So the cats can knock it over?
Nora: No, put in the... sink... trash... hmm...
Me: Does ice cream go in the sink or trash?
Nora: [whispers] For real, can you tell me?
Me: Leftover ice cream goes in the sink, because it melts, and liquids go in the sink.
Nora: [confidently] You carry the ice cream over to the sink, put it in the sink, leave the bowl in the sink, and then you're done!

[4] I do some of this with adults as well, as a big part of my sense of humor. It's not a considered approach to building skepticism, just what comes naturally. I think some of this is from my upbringing, in a very "questioning is a form of respect "culture (influenced by both the Quaker and Jewish sides of the family).