Unless he is mentally impaired, her DH knew good and well he needed to get his rear end back to the house and help out. But did he do that? No, he called home and pestered her like a little boy asking his mommy if he can play with the kids down the street for just a teeeeeeeeeeny bit longer.....and probably had his bottom lip sticking out when he asked it.

He wanted her to be the mommy and either give him a "get out of jail free" card or turn her into the big bad wolf by forcing her to ask him to PLEASE come home and help out.
I would have never asked him to "please" come home. More likely I would have said, "I cannot even believe you have the nerve to ask me if you can stay longer. I'm at home sick as a dog, one of the kids is getting sicker by the minute and YOU want to stay out and play. I would think any responsible husband and father would KNOW what he needed to do, but here you are calling and asking. I'm not your mama and you don't need to ask my permission to stay, but I am your wife and you will have to live with the consequences if you chose to stay and play instead of doing your job as a husband and father. You'd better think long and hard about what you do next." CLICK.
I don't believe in being passive aggressive or beating around the bush. I say what I mean and I mean what I say. Then again, my husband would never have left me and DD at home in the first place, had we been sick. It would have never crossed his mind to be so selfish. Thank God.
Don't let him turn you into the mean old mommy. Make it plain that he's an adult and he needs to act like one. Whatever decision he makes, he lives with the fallout. That's life.