If the health visitor is calling why would you need to interfere?
Children do scream and cry A LOT, I know our house sounded like someone was being killed when I was little and I've not really been out in my garden since last year because of the weather, so why would they perhaps?
I understand that you are keen to make sure nothing is amiss, but the lady doesn't have to go out a regimented amount of times if she doesn't wish to, or answer her own front door if she doesn't want to, and different cultures have different social norms too. As you said her husband words in a take away, are the family British or immigrants? If they are immigrants perhaps she doesn't have a strong command of English, and thus shies away from going out or keeping appointments?
Lots of reasons for everything that you think is suspicious and if the kids look healthy, happy and the health visitor calls then I'd be vary of stirring up trouble for people.