Are you possibly
a SOFTWARE PROGRAM (or computer program/software in general)
Everything is known about me
Assuming one has access to the source code, everything is known about the software. It's not like an animal or the weather, that can do something unexpected or on its own. Software can only do what it is coded to do.
From my eating habits
Software's 'eating habits' are to consume input and release output. This process results in known behavior, based on the coded logic.
to my family
Software will belong to a family of like software that has a reasonably consistent set of rules/language/compilers, etc. For example "JAVA", "C#", "COBOL" could be families. The family is typically documented and well known.
You can kill my parent and children
I would not be scared, but I would still run
Software can be triggered by a parent process. Often if you kill that process, it will still run (unless you killed the OS/compiler itself, etc.)
Software can spawn child processes. Often if you kill the children, the software will continue to execute. In both cases, the software is not scared.
I can be malicious, I can be nice
Software like viruses or malicious software, for example, are bad. Software like commercial or non profit sites, for example, can be nice and helpful.
Bringing a world of hurt,
Malicious software can cause extensive damage to financial systems, personal lives, governments, etc.
or a very cool mice
Software can be used to create neat things such as a super souped up computer mouse.
Maybe now that you've learned more about me
You'll start noticing how important I can be
In this day and age, software is quite useful and important for everyday life.
What am I?
You are a SOFTWARE PROGRAM!