What it really boils down to is as others have said - they're better to read about than to actually play.
By their nature, they're constantly A) stealing from their companions, B) getting themselves into danger which the other PCs are obligated to get them out of, and C) doing things that put both them AND the other PCs in danger. Even though these problems arn't intentional, arn't malicious, doesn't excuse the fact that they happen. Regularly.
Adventuring's dangerous stuff, and trust in your companions is a huge deal, because your life is very likely to come to depend on it at some point. Kender, whether they mean it or not, cannot be trusted in that way. They're flakey and they steal from you.
If there was a human character that was flakey, stole from everyone, and kept landing everyone in hot water time and again, nobody in their right mind would tolerate them in the group. But for some reason some folks expect people to put up with that behavior from kender just because oh, that's just their quirky nature.
No, nothing doing. Doesn't matter who's doing it. Intolerable is intolerable, period. *nod*