The real problem is not a lack of focus when something amuses them they can stick with it, it is their constant curosty and that when they do something they focus on it 100% IE when the pick something up it has 100% of their attion then they notice something else it gets 100% of their focus so they forget about the first thing and place it in their pockets.
Now in some groups or done right they can be good charters, but often some one is over disruptive with what they do as a kender. Playing a kender right in a maner that is not disruptive to an over all group is realy hard to do.
In shadow run they whould be overly curious and get themselfs and the group killed.
On the pluss side if you are ever short on ammo in a run ask the kender for it and he will probaly have it pre-loaded in magazines just like the ones you lost.