I think you have to stop looking at individual incidents and look at the child's life as a whole. For example a child who does dangerous and risky things, does her life have a place where she can do risky things safely with supervision or is she living in a protected environment and so just trying out her natural spirit of adventure whenever she can? Introducing something like climbing might help.
If a child is hitting and seems to enjoy hurting others, is that really the reason? If so where did he learn this was enjoyable? Inflicting pain on others (or oneself) is sometimes a way of coping with emotions we can't handle. Of course the child has to be stopped, but other measures need to go into place as well if there is a pattern. Praise and positive reinforcement of kind actions, discussion of how the child is feeling and a recognition that children do have dark moods which they need help to cope with all help.
M0nica I think sometimes you do need to explain to children that they are not adults and yes adults sometimes do things children don't like. If it's something that can be discussed because it is questionable (say something like smoking) then you will discuss it and try to change, but if it is a situation which involves safety or impacts on family life, then the adult takes precedence (point out she'll benefit from that when she is older). As for the dangerous, see suggestion above.