My child had kawasaki disease. Now is it coming back or is it the flu?

Something else. Very unlikely for someone to have kd twice but not impossible. Most likely it is something else though. Definitely see your pediatrician.
One time. Kawasaki disease is a one time only disease. Many other illnesses can somewhat resemble kawasaki disease. Best to have your child evaluated.

Related Questions

Is there a relation between kawasaki disease and dengue hemorrhagic fever?

No. Dengue hemorrhagic fever is caused by one of four different dengue viruses and it is transmitted by mosquitoes. The cause of kawasaki disease remains unknown. The symptoms and course of the diseases is also very different.