Thanks for your query.
your child is having high grade fever with some exanthematous rash
,i advise you to take him to pediatrician
for evaluation,in the meantime give paracetamol
every 6 hours,do tepid sponging,give him plenty of fluids,you can apply calamine
lotion 3 to 4 times a day over rashes.
Your son will be fine soon.