I had a dcgirl with "thrush" once. Only it was misdiagnosed. It was actually hand-foot-and-mouth disease. I sort of wondered but when EVERY one of my dckids came down with it about 3 days later I KNEW it was misdiagnosed.

Don't trust doctor's diagnoses - they are often wrong and they almost always tell the parents it's okay for the kid to attend daycare. Well, it is MY (YOUR) daycare and YOU make the rules as to when and who attends. So, in this case you should have sent that kid home.

I find it VERY unlikely that a 15 mth old would have thrush. It's likely NOT trush. It's more likely HFM or strep.