30Mph is 30 for a reason. You can stop at relativly short distance at 30 and put simply when a road is at 30 and school is chucking out or you are going down a high street you are processing a hell of a lot of information, a child stepping could be information overload and you have a delayed reaction.
Personally i could never live with myself if i killed a child, but i guess if you know that you could then go right ahead. You are more dangerous than the guy doing 100mph down an A road IMHO. Least if the guy crashed on an A road he would crash into another big metal car. At 30, you crash your big tonne and a half weight travelling at 30, (maybe slightly less if you braked but you could not have seen the child run out between parked cars) straight into a child with no protection. That child has just had a face full of your radiator/bumper, nice. He/She's dead or got permanent damage (Mental/Emotional/Physical) for the REST OF THEIR LIFE. You cock.
Graham