Don't get me wrong, I'm all for avoiding unnecessary conflict. And a lot of conflict avoidance with kids is to not let them turn it into a conflict. You said no, you didn't start a fight.
My kids are 2,3, and 4. No works just fine for now, and we are laying the foundations for budgeting.
Not even Doom music!
I really don't appreciate your reply. It comes off as assuming that I'm basically an idiot. "Oh, just tell the children no!" Yeah, that doesn't really work when you have highly intelligent children you've been raising to be rational, thinking agents. They may not be developed enough to value long-term health issues over short-term pleasure gains yet, but they certainly are skeptical enough to call out fiat answers as bullshit. I'm actually rather proud my children argue with me so much, despite how exhausting it can be.
Hence me targeting my ire at the damn ice cream truck. It's not my children's fault they want ice cream (they are children) or that they are elementary school lawyers (I have certainly encouraged it, much to my in-laws' ire). It is the ice cream truck operator's fault for employing marketing tactics aimed directly at children. I keep my children off of cable TV and pay for streaming subscriptions to keep them away from completely unadulterated junk until they have brains developed enough to see through it, but this guy injects it out of my control.
It was specifically the use of the words "guilty" and "whining" that struck me as wrong there. I could see wanting to avoid seeing disappointment. But I don't consider that guilt. And I'm pretty strict on my kids when they start whining.
This one is an odd area where I would think budgeting would be a good lesson. Set a budget aside for how much they can spend per day and per month on ice cream. If they have the funds, they can get it. If not, make it clear on when they exhausted their budget. In this regard, it should not be an open question on whether or not they can get something. And any "no" will be a direct result of something they have control over.