Is the thrush in his mouth and due to breast feeding? That's really the only kind I'm familiar with...first of all, I certainly wouldn't appreciate a parent dropping off a kid with thrush without talking to me about it first. And it depends on the age and everything, if he is young and mouthing everything but has thrush in his mouth that would really erk me, if I were you I would be tempted to request a doctors note stating that he is not contagious and may attend daycare. Maybe the rest of the ladies here have more knowledge...