Impeach him. Twice.

It’s a natural stage of development. Playing with the idea of reality is part of understanding and accepting the world around them. Let them play in the world of make believe while asking them about what they’re experiencing and help them form understanding. *Pointing to blue item “This is orange.” “That’s orange? What else is orange?” If they demand you agree with them, it should be fine. This is early development. It’s way, way more important that they feel safe and loved than what they’re thinking and saying. They will grow and if they seem to be too distant from reality, there’s plenty more things you can do to help them at that stage.

I’m not a parent but a teacher who has encountered similar things with students. This won’t work in all the situations you described but you can try giving them affirmation by telling them they are very creative for coming up with cool ideas or stories. This can provide positive attention without conceding the point.

Also for some things like ice cream not being cold, you get explore the idea with them. Cold is, in fact, not a thing, it is just a lack of heat.

I would always agree and amplify.

Toddler: Snow isn’t white

Me: really? And all this time I was wrong? Now I see it, it’s pink! Unicorn and rainbow pink! And grass is also pink! And water too! Everything is pink!

Just have some good laughs.

Feelings of others is more difficult and you need to be delicate to teach them respect and empathy.

But doing it in a forceful manner often has the opposite effect.

The problem with direct pushing back is that

Not a parent, but personally I would also err on the side of correcting them, as they’re still heavily exploring the world. Partially, they’re figuring out the world by making statements they believe to be wrong and do actually want you to confirm that they’re wrong.

But yeah, if they’re throwing a tantrum, they may rather be looking for more input than that. More attention or a playfight of wits even, so to speak.
Asking them “why?” as many others suggested, seems like a good start here.

Personally, I would also try just feeding them tons of information, like if they say that snow isn’t white, tell them that it is, because it reflects all the wavelengths of light. Obviously, they won’t understand what that actually means, but it gives them something to think about and in the sense of the playfight, they’ll be satisfied, too (i.e. defeated and learned something).

My child does this too sometimes, it’s sometimes a form of testing their own power over the world and sometimes odd humour .

If it’s obviously a deliberately false statement I tend to dismiss them with some form of “Don’t be silly” or “Poppycock”. Not arguing, but dismissing something as silly can be more effective.

It’s fine. I wouldn’t just ignore it though. Maybe question why they think these things. ‘What makes you sure he’s not hungry? Did you ask him?’, ‘Are you sure she didn’t want to sing? I think she has a pretty voice.’

Your toddler is coughing e their desires more than denying facts. If anything, it’s an expression of imagination and should be encouraged with guidance away from just telling outright lies.

my kid used to deny my own personal opinions, it almost always pissed me off at first. I felt like I was giving so much and I didn’t want to give up my opinions too, simple things like me saying that I like something could provoke him to argue that I don’t. My spouse helped a lot, we made it into a family joke like he’s a little dictator, maybe he picked up on the laughing and learned that it was inappropriate behavior.

Is his name Donald, by any chance?

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Lots of good answers here, but I have a slightly different interpretation. This may be something that catches some flack, but reserve judgement until I am done. Maybe your kid is actually a genius. Like a bonified genius, no sarcasm. He sounds a lot like I did when I was his age and it turned out that I am actually somewhere in the top 0.03% of the population. This is not a brag, having this means I have a lot of unique mental health and social issues I have to deal with.

What leads me to the thought are the specific examples he gave. Fundamentally, all of the observations are 100% true.

• Snow isn’t white. Snow is clear, but the way light reflects internally when you stack it up causes nearly 100% of white light to be reflected, which is what makes it look white.
• Ice cream is not cold, as cold is merely a word that describes an absence of heat. The concept of cold is 100% subjective and reliant on a comparison. In essence, you are having a problem with your child’s opinion, which you complained about him having issues with yours. Until you get down below about 30°K, you can’t really say something is objectively cold, as that os where the laws of physics start changing (condensed matter, superconductivity, etc.).
• “It’s not dark yet.” this one is fun on two sides. First, there is a scientifically proven link between what we are taught as a concept of a word and how our brain actually interprets sensory data related to that word. There are societies who do not have words for particular colors, and when tested to identify a differently colored box amongst several boxes with a close hue, they are functionally incapable of discerning the difference. After being taught words to describe the colors and shown examples, they saw a marked improvement in identification. What this can functionally mean is that what you actually perceive as a light level that relates to “being dark” can affect how much of the light that enters your eyes is interpreted as “dark”. Your child does not have this limitation, so his threshold may be much lower than yours. This leads to the second interesting point, it is nearly impossible to create a space that can be occupied that is actually devoid of photons bouncing around. This fact, coupled with your child’s higher sensitivity to light, means that for them, it is actually not dark yet. You are seeing the world through an adult’s lens which says “it is night, so it is dark” instead of the child’s lens that says “dark means there isn’t light, I see light, so it is not dark.”

Even the issues they have with what is known as “sense of other” is an indication. Many geniuses struggle with the concept that other people do not share an identical physical, emotional, or mental condition with themselves. When he says “You’re not hungry” he is really saying “I’m not hungry, so that means you must not be either.” If they are a genius and has that affect, then this will be an uphill battle. Patience and getting them to understand that other people have their own separate thoughts and identities that are vastly different to the point of being incomparable will feel very surreal. It will also have the knock-on effect of making it very hard to directly relate to neurotypical people. My wife and I struggle constantly because I have such a different view of the world than anyone she has ever known.

The minimum age to be tested by Mensa is 4, so it might be worth reaching out to your local chapter and inquiring.

I’m with your husband. Your cold is trying to figure out where the boundaries here are. Unless you want to create a serial liar, the only reasonable answer is that you don’t tolerate lies. You don’t have to argue, you don’t have to get the kid to agree, but correcting them is reasonable and probably the right move, even if you do it in a sort of casually dismissive way.