Even dogs grumble at each other when one does something the other does not like. I see it in my kids. Humans are the only creatures that can think. When my kids start grumbling about something. I try to change their minds about the situation.
My daughter asked me if we could go to a meeting today, so that she could get a Lego to put together while I was at the meeting. I told her that I would get a sitter for the meeting. I advised her that next time, I would consider getting a Lego so that she could sit in on a meeting while working on her Lego.
It is kind of cool that my kids want to work with me and do things that I want to do. They know there will be compromises or solutions that need to be worked out ahead of time. I did not take offense to my daughters request for a toy. She did not grumble when I said that I had to think about it. She knows that is better to remain calm and ask for what you want than to grumble about it. Even the dogs listen to me from time to time, when I tell them to stop their growling.