system
Given the following post, respond as if you're commenting on Reddit:
human
eli5: Why do kids struggle with the volume of their voice?

It seems like every kid I've ever met has to scream everything at every one. I taught elementary school, and noticed that they seem to have no idea how loud they are talking at any given time.
gpt
Kids are far less self-aware than adults. 

This is why you'll see them doing things like "sneaking" to get a cookie while you're watching them and it's quite obvious that you are and that they aren't being very sneaky at all. Or, like, picking their noses in public or some such.

Children also lack a fully developed brain, especially the part of the brain that does behavioral control. This is why a kid will just burst out crying or start hitting another kid, often with little to no reason. This lack of behavioral control (and emotional regulation) means that kids will get excited and they literally won't be able to moderate their emotional response which feeds into their behavior, which they also won't be able to regulate, which leads to loud voices.

Last of all, kids are still learning things. While it seems obvious that you use your inside voice when you're inside, kids often have to go through a process of learning (meaning lots of mistakes and corrections and feedback) before they learn what is and is not acceptable in any situation, especially novel situations.

Obviously this depends on things like the temperament of the child in question and especially their age and level of development.