I would also refer to your own sick policy. If it's something highly contagious, I would close. I don't think it's fair to stay open and risk the others getting sick and than asking them to stay home until they're better. If you get paid sick days than it's up to you to decide if you want to use your children's illnesses for this or if you want your husband to use his (if he gets any).

If your daycare is separate or if you have a backup provider than that would be ideal and definitely mention that in your contract.

I'm sure most parents who choose home daycare are aware that the providers sick children may be a risk to theirs as well though.