In general Kobald are ment to be fodder. That is to say that kobald are monsters that are incountered in group for PC 1st-3rd level. If handled correctly with leaders, they pose a threat to 5th-6th level PC easily.
The formentioned is very true. I have experience such stories as DM and player. One of my favorite tricks is to let the fighter finnally have a wack at a kobald. He goes charging in only to find that the kobald is a half-dragon kobald barbarian with a full blade. "Ow that hurt! Run!"