Let's talk thrush

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DS has had what I thought was milk coating his tongue.  It's not on the tip, just far enough back that I can't really reach it, as he's not obliging enough to stick his tongue out for me and hold it there.  Anyway, I will be calling the pedi tomorrow, but who else has dealt with this, and how did you know it was thrush?  I feel bad because it's been there for a while now.  How easy was it to get rid of?  TIA.