I would imagine the couple's previous children will end up caring for the child. Like many alternative familial arrangements, it doesn't bother me all that much if the children live in a strongly bonded large family group and will be raised in a household where there will be others to take up a part of the childcare. I imagine the parents' other children will end up doing the bulk of the care of these children anyway. I think it was somewhat unnecessary just to have a male heir, but I also live in the US and haven't been subject to that cultural pressure.
I think it's probably a different situation than in the US where you have two parents and the children living in relative isolation from the rest of their family, so it's slightly different. This is an assumption, of course. I guess as long as the children are provided for financially and emotionally I'm not too worried about how old the biological parents are.