Honestly, I have nothing against kids so long they are well behaved. However, after had a job in an environment filled with a lot of families and younger children I must say that I'm always completely baffled to see how poorly some parents raise their kids - to the point where you start wondering why some people even got kids if they're just gonna leave them at a playground area first thing they do and completely ignore them when the kid screams across a room filled with customers for their parents to come and look at them.
Not all kids are bad, no. I don't hate them either. I don't have any myself and don't really have any plans to get myself some either in any foreseeable future, but some of my friends as well as friends of my family has some adorable and extremely nice well-disciplined children. It's just that there's a lot of parents out there, to my experience, that are doing a bad job at raising their children properly (seriously, parents, your phone is NOT supposed to me more important that your child!) and thus I'd say is why so many kids these days seem to end up behaving so poorly.
A lot of bullies tend to be kids too, I was mildly bullied in my youth by kids that were only a year or two older than me, so I see your point. Again though, not all kids are angels, unfortunately.
I find that these bullies are often the product of bad parenting, the ones with really good parents either being around the wrong people or simply failing to realize that they are actually bullying someone they though they were just playing with (i.e. going too far, many times caused by one or another form of mental disorder).
I do try to avoid kids I don't know. Not because I hate them but rather because I, less and less, trust the parenting skills of any strangers by default.
Thus, for most bad-behaved children; I blame the parents, not the kids.