I found this info on the Dept. of Health and Human services website:
What problems can occur after chickenpox vaccination?
Soreness, redness, or swelling where the shot was given is the most common side effect, occurring in about 20% of recipients.
About 1%-4% of vaccine recipients develop a very mild rash or several small bumps following chickenpox vaccination. [NOTE: In very rare instances, it may be possible for someone who gets a rash from the chickenpox vaccine to transmit vaccine virus chickenpox to another person. Persons developing a rash after vaccination should take extra precautions to avoid contact with anyone whose immune system is not working properly.
The vaccine may cause a mild fever 2 weeks after vaccination.
A seizure (jerking and staring spell) usually caused by fever may occur in less than 1 in 1000 vaccine recipients. This may not be related to the vaccine.
I do know also if the child was coming down with something or already carring a bug, that get a live vaccine, like the chickenpox vaccine, can send the immune system into overload, resulting in fevers to fight it off. I would give it a little longer, and if the problems don't resolve, demand the doctor to do something. Bug them to death until they do.