Many of the children who are employed as helpers, messengers, cash boys and minor laborers in shops, foundries, factories, offices and as venders, are the mainstay of families that live, God knows how, for the one who should be the bread winner is an invalid, a cripple, a paralytic, and would be in the charity hospital or the almshouse were it not that the instinct of family unity is as strong and admirable among the humble as among the rich.
I don't understand what "were it not that" & the last part mean. Does it mean that "it's not because that the instinct of poor families are as strong as the rich families, but thanks to the children, poor families are able to live"?