I'm going to focus on the 'nice' children (from your second post) who talk a lot, are hyper and shout out. These things are examples of low level disruption but it does make a noticeable difference and doesn't help create a good learning environment for all 30 (or more) pupils in your class. 'Nice' children may be polite and overall lovely but their behaviour can also be considered inconsiderate/rude if their behaviour impacts on the learning of the rest of the class, whether they intended to or not.
From my experience as a trainee science teacher so far, I wouldn't use the word 'bad' but 'disruptive' instead because children are children, not bad or good, they're still young and learning. It's all about poor pupil behaviour and definitely not the child being 'bad'.
Talking: it's important to consider whether this is (1) during instruction time when the whole class needs to pay attention, be quiet (don't talk) and listen to the teacher, or (2) during an activity which allows quiet chatter as long as work is completed or (3) during a silent task (where no one should be talking unless hands are up and they're discussing something with the teacher or TA).
Instruction time
I notice a domino effect in some classes during instruction time where a couple of pupils may be talking about the work but when they're not told to be quiet, this inspires irrelevant talking by another group of pupils who think it's ok to talk over the teacher/ don't realise the first couple of pupils were talking about relevant information and that's why the teacher didn't say anything initially. When the domino effect spreads to a good number of the class though, you can see clearly that pupils aren't paying attention where they should, they're missing key information and need refocusing.
Ultimately whether pupils are talking about the work or something irrelevant during instruction time, they need to be quiet and pay attention, then put their hand up to clarify things with the teacher as needed. I've learnt that when I teach, I need everyone focusing on what I'm saying during instruction time to give them the best learning experience. If you are interested op, you might want to look into the idea of germane, extraneous and instrinsic cognitive loads to work out why pupils talking when the teacher is, regardless of the pupil doing the work they should be doing, isn't great for their learning or another pupil next to them or nearby.
Talking during activities
No one should be talking during silent activities.
During non silent activities some pupils might talk a lot and do their work and that's good for them. There's a problem when they end up disrupting the learning of other pupils though. Some pupils really struggle concentrating with background noise. Some pupils want to do the work but struggle to get started and anyone talking nearby is the perfect opportunity for them to procrastinate.
Hyper and shouting out: Shouting out is not good. As a teacher you want the class to be calm and focused on learning and doing their best. When one person shouts out, you get a domino effect again where other people think it's ok to do that if the initial shouter isn't told not to. As for hyper, enthusiasm for learning is fantastic but not for the other 29 pupils if it ruins the atmospheric Feng Shui of the class/ doesn't create a positive, calm learning environment for all.
Looking back, I didn't mean to write so much 
but I hope it helps to see things in another way.