Oh no! I'm sorry to hear this. It can often be the case if they are a bit run down. Have you got any cream to put on it? Whereabouts is the patch? If it is not near eyes, nose and mouth you can get shampoo's that will clear it quickly, but these have to be prescribed by the vet.
I'm sorry you're having such a bad time of it at the moment with your little ones

. Hopefully this will be the last of it.
How are their weights now? Are they picking up at all?