I agree with PP, tell him in advance, because him kicking off and arguing over a poorly girl on the doorstep won't be in her interests.
Keep it factual, re: what she has, and that you've informed the nursery that she can't go back for x days. He doesn't need telling what he needs to get in, he can figure it out himself, he has a working brain (allegedly).
Log his response, because it's unlikely to be thanking you for letting him know and he'll keep a close eye on her...