My perspective on our meat birds is similar to that of the produce I grow in my veg garden, and this is the viewpoint I try to share with my children. We often see them sprout/hatch, we provide for their needs, we protect them from harm, we admire their beauty, are impressed with their growth, and appreciate them immensely when they are harvested & consumed. That is their purpose in this world, we don't take them for granted, nor the enormous amount of effort needed to get them to the table, and therefore we are extremely grateful for them and do not waste a morsel.
Still, my youngest is already 7, and he and his brothers won't let me name the meat birds, not even something obvious like "Drumstick", and we don't eat our familiar & named layers. You may not want to connect the dots too clearly for your 3 & 4-year-olds right now, between this named but aggressive rooster and your next chicken dinner. You can just say that this roo's behavior is too rough for the rest of the flock and he will have to "go".
Personally, I wouldn't encourage the idea that only "bad" animals are for food. Animals aren't good or bad, they just follow their instincts. Some are more aggressive, or fearful & wary, and their behavior is dangerous or unpredictable. But many livestock animals are sweet natured and gentle right up to the moment they're processed. Nevertheless, their purpose is to be food, and their nice temperment just makes the job a little easier for the person doing the processing.
Let us know how things go with this roo & your girls!