Everyone's favorite poker saying is "It depends", and never has it applied more than here. However, I'll try to give you some general advice:
There are 2 reasons to raise on 3rd street. Reason #1 is to thin the field. Reason #2 is for value. In the situation you describe, if there are several limpers already in, and its unlikely that any of them fold to a completion, then you can't thin the field. Also, since both of your kings are dead, we're not a very big favorite over the field, so we really can't raise for value. So the play would be to either fold, or call and keep the pot small.
Limping behind with dead kings allows you to disguise your hand, and keep the pot small. Keeping the pot small allows you to fold on later streets more easily, and it gives you more fold equity on later streets if you later want to thin the field. Additionally, because you "slow-played" your hand, players may bet into you on 4th/5th, allowing you to raise and then knock out those pesky limpers. Or they may incorrectly put you on a hand like a 3-flush, and play incorrectly against you.
The choice of folding or calling should depend on many things, in order of importance:
1) The number of players in the pot, and the door cards behind you. If there's 2 limpers in, and you only have the bring in after you, we're most certainly playing (and maybe even raising). If there are 3 limpers in, and there's a live ace to act after you, then we're almost certainly folding.
2) The quality of your kicker. K♠ Q♠ - K♥ with all the spades, aces, queens, jacks, and tens live is a much different hand from K♣ 2♦ - K♠ with all the kings and deuces dead. Having a straight flush kicker (with your flush suit in the hole) that is totally live allows your hand to play much stronger in a multi-way pot. The worse your kicker, and the more limpers there are, the more inclined you should be to fold.
3) Other crap like the size of the antes & bring in, how aggressive the game is playing, ect. If your opponents are easy to read & manipulate, and the antes are super large, obviously we should be more inclined to play.
In "7-card stud for advanced players", Sklansky goes pretty in-depth into situations like these, so consult his book for more reading.
So um, yeah. It depends. But (as you probably know by now) the Stud games are ALL ABOUT "It Depends". Hands can be horrible or awesome, depending on the upcards and the number of players in the pot. So get used to analyzing all these factors when choosing to play/fold on 3rd street.
