Thank you for your query.
I suggest that you discuss with your doctor and get your son investigated. Simple investigations can direct to the right course of management and the cause of the fever
Your observation that your son is catching an infection from the play school is correct. At this age the immunity of a child is low and he would tend to contract infections frequently. This is a very normal phenomenon and you need not worry on this count.
I hope I have answered your query to your satisfaction.
Wishing your son an early recovery.
Rajiv K Khandelwal