The children make us sick more often than we could possibly contract a sickness anywhere else, that's a fact! My sick policy is very strict regarding certain things like fevers and infections to force parents to take their child to a doctor, but a virus is a virus and they are everywhere and can't be escaped. It will run through a daycare over and over, runny noses can't be helped and it really doesn't matter who gets it first.
If you are sick or your child is sick you have to close for a day without pay unless you have written paid personal sick days into your contract. If the child you care for is sick with the flu they have to stay home and they have to pay, but I hope you put that into your contract.