Well here's my 2 cents worth.....

I absolutely believe it is the responsibility of the FA to maintain the environment of all cabins on an airplane. While there can be little done about a crying child, there can be plenty done about bad behaviours, and we all have the right to request a certain modicum of behaviour while we are flying.
Although I agree that adults can/are just as annoying in FC, their behaviours are controlled by societal values(i.e. threats of legal measures, etc). For instance, an adult that willfully throws food or drink on a fellow passenger would be appropriately dealt with (because they supposedly understand the ramifications...though sometimes I wonder).
In the case of a child doing the same act (which I have witnessed on different occasions) , the only control mechanism is their guardian. At the time of the act...be it repeated thumping on seats, screaming, bratty outbursts, etc, we all have the right to request the FA to step in. When an adult exhibits inappropriate behaviour, we have no trouble requesting assistance, right?
In other words...misbehaved children are the responsibility of their parents, and any problems should be directed to them. And in my eyes, this is one of the duties of the FA.

Now just to be clear....I have great admiration for parents that must fly with their children, and greater admiration for those that think out the process before they embark on this voyage. However, before booking your children into FC think about how enjoyable the trip will be for you and your children, the added stress of your fellow passenger's anger, and how you would feel if you were in the reverse position.