Monsoon season between June and August is the best time to visit Kerala for Ayurveda treatments but if you are looking for day activities, you might be stuck in rain the entire time. Instead plan to any beach side for June-July.
Kerala is a wonderful Destination...
and in mansoon it looks even attractive...
but please go in first half of june... after 1st or 2nd rain...
because kerala has heavy rainfall and if u delay, it may spoil you mood to visit the nature