Kidney function tests should be done at regular intervals to rule out kidney
involvement (if kidney
gets involved, yes it can become serious). Usually there is accompanying stomach and joint pain.
Fever with rash can also be due to viral fevers, dengue, typhoid, malaria, and H1N1 infection. It can be due to measles, chicken pox, or due to group A streptococcal infection. Hence all these should be ruled out. Please discuss with your child's treating doctor.