A cracked head is indeed rare without any evidence of trauma or abuse. Especially on an engine that is well broken in and has been driven conservatively. I would suspect the possibility that the head bolts might have been too tight, but...that also depends on where the crack actually is. Have they told you where it is? Some cracks can be welded if they do not penetrate more than one surface of a water jacket, but usually is is a better bet to replace the head. What you do from here depends on how much you want to spend. How much do you love your car and how long are you going to keep it for. If you really want to keep it, the a new or reman head is the ticket.
2000 Dodge Grand Caravan SE
No matter what you fix, there will always be something else to fix..
"Warranty" is just another way of postponing the inevitable.