My son has tonsillitis ad high temperature. can i give him cold stuff like icecream, yoghurt or some warm water? warm towel compress?

Worse: Cold things can increase metabolic activity (=temperature) as body warms them up and maintains its temperature. "tepid" rag (~90-95f) to skin will help cool--don't use too cool water as will cause shivering and increase body temp. Sounds like needs seen in er / urgent care.

Antibiotics?: An important cause of tonsillitis with fever is group a streptococcal infection, also known as strep throat. It is important that this diagnosis be made and treated with a penicillin. Treatment of strep throat with antibiotics decreases the likelihood of development of rheumatic fever, which is the important reason for strep throat care.