To keep 1 DC home from school when the other 3 are ill

[Rudolphsnose]

Really not sure on this one.

2 of the 3 DDs and DS are ill (as am I), really nasty cold and coughs so the DDs aren't in school, DS is 15mo.

AIBU to keep the well DD home from school saving me and the other DC going out in the cold?

I don't think it will be the end of the world, if you did this occasionally. If the Dc are ill for more than a couple of days, I'd try to get someone to either sit with the ill children or do the school run for you.