Greetings.
This is acute urticaria. Could be due to any infection / viral fever or contact with allergenic substance.
See a qualified dermatologist / pediatrician and treat the child or urticaria and fever at the earliest, Warm regards, Dr Govind Suresh Mittal. Bengaluru.
Health Tips
Caution : see a qualified dermatologist / pediatrician and don't be lured by quacks who aren't qualified doctors.