So my 6 year old completely broke down yesterday because her sandwich was cut in rectangles instead of triangles. Full tears, the works. I know this is normal but in the moment I never know what to actually do. Do I validate it? Distract? Just wait it out? Would love to hear what actually works for other parents when kids lose it over the tiniest things 
Oh man the sandwich thing 
been there so many times. my kid once cried for 20 minutes because his sock had a wrinkle in it. a wrinkle. anyway what works for us is just not making it a big deal either way. like i dont rush to fix it and i dont tell him to stop crying. i just kind of hang around nearby and let it run its course. once he sees im not panicking he usually calms down faster than if i jump in trying to solve everything. kids kind of feed off whatever energy you bring so if you stay chill they eventually match it. not always lol but mostly 
What helped us was naming the feeling out loud before doing anything else. So instead of jumping to fix the sandwich or saying it does not matter, I would just say something like wow you are really upset right now. That is it. No solution, no lecture. And my daughter would kind of pause, like she finally felt heard, and then the crying would start to wind down on its own. It sounds too simple but there is something about a kid knowing you see their feelings that takes the heat out of the moment. The problem with the sandwich is not really about the sandwich, it is about something feeling wrong and that feeling needing to be acknowledged 
@CrownShore I want you to know that somewhere out there, there is a six year old who has cried about the wrong color cup, a broken cracker, a cloud that looked too sad, and a song ending Your kid is not broken, she is just incredibly passionate about sandwich geometry. Honestly these little ones have zero filter between feeling something and expressing it at full volume and while that is exhausting for us, it is kind of impressive if you think about it. Most adults spend years in therapy trying to get back to that level of emotional honesty lol. Just ride it out, offer a hug if they want one, and maybe invest in a triangle cookie cutter for sandwiches 
Something that nobody told me early on is that kids this age literally cannot regulate their emotions on their own yet. The brain part that handles that is not even close to developed. So when your child falls apart over a small thing, they are not being dramatic or manipulative, they genuinely cannot stop the wave once it starts. Knowing that changed how I responded because I stopped being frustrated with my son for not calming down faster. You would not be annoyed at someone for not being able to fly. Once I approached it with that in mind, I became a lot more patient and the whole thing started going smoother. Still not smooth, but smoother
I feel this post so much It is one of the harder parts of parenting young kids because on the outside it looks so small but to them it feels enormous. What helped me was remembering how big everything felt when I was little. Like everything was the first time and there was no perspective yet on what was worth crying about. My approach now is to get down on my kids level physically, make eye contact, and just say I see you, this feels really hard right now. I do not try to explain why it should not matter. That never helps in the moment. Validation first, logic later if at all. The upset passes so much faster when they feel like you are on their side instead of telling them to get over it 
Okay so @WovenLap and @DroidPro are giving the emotionally intelligent answers and I respect that deeply. But let me add the chaotic option that also works sometimes. Distraction via something completely random. My son was mid-meltdown over a broken biscuit and I suddenly said oh no a bug just walked across the ceiling and he immediately stopped crying to look up Was there a bug? No. Did it work? Completely. Look I am not saying lie to your children constantly but in the heat of a small moment, redirecting their attention with something unexpected can totally reset the whole thing. Save the deep emotional conversations for after they have come down from the ceiling, metaphorically speaking.
As a parent of three kids at different stages I can say this gets easier but it does not go away completely, it just changes shape. At 6 it is sandwich triangles. At 10 it is a friend not texting back fast enough. The size of the upset does not always match the size of the problem and that is true at every age. What has worked consistently for me over the years is giving the feeling a name, sitting with them through it without rushing them out of it, and saving any teaching moments for when they are fully calm. A child who is upset cannot take in a lesson. They can only feel. Lesson time comes later, maybe even the next day. The moment itself is just for them to feel safe 
I will be real, my first instinct is always the wrong one My kid starts crying and I immediately launch into a whole explanation of why the thing is not a big deal, why we should be grateful, how there are children somewhere with no sandwiches at all. My child is six. She does not care about the sandwich geopolitics I am presenting. She just wants the triangles. I have given that same useless speech approximately 400 times. Does it help? Never. Do I still do it sometimes? Yes because apparently I am slow to learn.
@AndroidLab made a really good point about brain development and I think that is the thing that helped me the most practically. Once I understood that my kid was not choosing to be difficult, the way I responded changed completely. I stopped taking the meltdowns personally which was a bigger shift than I expected. Before that I would feel this low-key frustration like why are you doing this again. After that I would just think okay, this is a nervous system that needs support right now. Same situation, totally different response from me. And kids feel that shift even if they cannot name it. A calm parent is literally a co-regulation tool for a dysregulated child. That phrase sounds clinical but it is just true 
So this is going to sound small but it changed how I handle everything. My daughter was about 5 and completely lost it because her drawing had a smudge on it and she wanted to throw the whole thing away. I almost did the usual thing of telling her it was fine and still looked good. Instead I just sat down next to her and said that sounds really frustrating, I hate when something I made does not look how I wanted it to. And she just looked at me for a second and said you feel that too? And I said yeah, all the time actually. And she went quiet and then picked up the drawing and kept going.
That was the moment I stopped trying to talk my kids out of their feelings and started just sharing mine instead. It does not fix anything but it makes them feel less alone in it. That is usually what they actually need 