Soooo.... when are you gonna carbon wrap every knife in your house? Put sponge on every sharp corner of the furniture, set up saftey nets at every window and on the stairs? When ypu leave the house do you wear armour in case you ge hit by a car?.....
It goes on and on, things are dangerous, its nature, yes we should do things to make stuff more safe, but un-expected and fatal dangers, not stuff like this. If your gonna be dumb enough to make the mistake again, or to try it out to see if the danger is still there, you absolutely deserve to have hands like Sir Ranulph Fiennes! Considering there is this pointlessly long thread about it I highly doubt that you will make the mistake again, so all of your effort to make a solution to the, pretty pathetic, problem has been rather pointless.
If it's to stop your kids doing it tell them not too, if they still do (which juding by the hoo har you have made out of it I don't think they will) it's their own fault and they will learn from their mistakes like you, and everyone else on the planet has. Or if you really want to make sure it doesn't happen do what you would with other sharp blades, like knifes, and put the bike somewhere they can't get to it, like say a locked shed.
Danger exists learn from it and deal with it.
P.s I am sorry about this snappy and quite angry reply but this thread has been raping my notifications for days on end.