I don't know about your experience, but in my experience it often takes a lot more than "telling them to communicate about it" to nurture considerate behaviour. Empathy needs to be built, especially when there's all the baggage of past inter-sibling dynamics, lingering resentments, hang-ups due to birth order and family roles, etc. I think that's what pek was alluding to: some ongoing support and guidance may be required from the parent in creating a considerate, empathic relationship over food treats. It may require a lot more than simply telling the kids to communicate. Not to say the parent needs to be in a police-like role, but there may be considerable support and facilitation required.
That's certainly true. Since we weren't being presented with any issues except food, I was optimistically assuming that the kids didn't have any other major sibling issues and had basic empathy for each other. And if not, those things were already being worked on. Of course, things like this food issues can be a symptom of the relationship rather than the actual issue... I can't guess how much facilitation and guidance is needed, not knowing the kids or their relationships. I think it can fall short of being the food police, though. And the kids communicating with each other is an excellent first step.
I know I have this easy with just one kid. But I have 6 siblings so I know what it's like having older siblings and younger ones, and there not being as much as we wanted of special foods. Half a kiwi was a treat! Counting heads and dividing by that is second nature to me. Buying a box of 8 ice cream sandwiches would automatically result in my saying "That's two per kid and one each for me and daddy." And by the time the kids were this age, they would be doing the math.
I'm taken aback when we go to other people's houses and the kids want to eat their special food in front of my ds without sharing. Or when a child who doesn't even like a food item in question complains that someone else is taking too much. So I know food issues are relatively normal but I'm surprised when kids don't have a grip on the basics, like don't eat all of something without asking and don't eat in front of others unless you are prepared to share. And the reason for those two things are other people's feelings. I guess the problem with siblings can be that they don't always care about each other's feelings.