Is it more or less tragic to murder an adult for what they have done or a child for what it hasn't but will or might do? If adults are inherently less innocent and all children grow up to be adults and thus lose their innocence along the way, then isn't it ultimately the same result, and thus more of an issue of timing?
To my mind, the idea of childhood innocence is that they've had less opportunities to do bad and have a lower quota, not that they haven't done bad period. So it's a bit of crock, like 'sanctity of life'. Equally, depending on the age of the child, they're quite capable of knowing what they're doing and the consequences, the difference is that they are to a certain extent sociopathic; they haven't yet been temperered by their social environment to conform and obey social rules. Kids love doing naughty things and do so out of curiosity, boredom or just because they can. In adulthood we learn to only do such if we can get away with it, as we are more fearful of the ramifications of being caught (embarassment, exclusion, financial penalty), kids aren't as bothered.
Imagination will often carry us to worlds that never were. But without it we go nowhere. - Carl Sagan