I'm still waiting to hear how you "finish it" when a kid has a weapon
Obviously the first thing to do would be to get away, but if necessary there are options available to you- a throat strike, for instance, or a kick to the knee. You can block and twist, you can go low (drop down to a crouch) and strike upwards, either to the groin, if it's 'open', or to push the weapon-holding arm up. You can stamp on a foot, stamp down the shin, or dodge to come round the back and strike in the kidneys.
You can block, grab the arm, twist it and use your other hand to force the attacker down to the floor by the shoulder.
I could go on, if you like. But the average 10 year old doesn't tend to have a weapon on them at playtime, fortunately, and so the above measures wouldn't be needed.
Most of the bullying I've heard of (and these come from students I have taught karate to) is pushing, hair-pulling and the odd punch to the stomach. Those kids that have been bullied, that come to us for training, are shown how to deflect first. Punching and kicking comes later, and only when we are certain that they've taken on the basic lesson first- that they never, ever, start a fight.