they're probably only raising the youngest few and the eldest siblings are picking up the slack in ways they can't even imagine - for eg: having sex talks, intervening with bullies, cooking/cleaning (most immigrant communities make elder children help out a lot here). So what's the point of having so many kids when you're making some of them raise the others for you?
But that's rubbish. That was your experience but why assume all large families are the same?
It is also quite offensive. My eldest children are not picking up any slack at all. Sex talks? All done by me and dh. Intervening with bullies? They have never done that. I do not make the older ones raise the younger ones, not even a little bit. I am the parent, I had them all and it is my responsibility to raise them and I do not put that onto the older children. I bet my children probably have less chores than most if anything. My eldest son does cook once a week but he is training to be a chef so he asks to do it and loves it and wants to do it more. The only cleaning they do is their own room and cleaning up any messes they make.
It is offensive, if I said only children were spoilt brats who grow into selfish adults there would be an uproar, but it's ok to say that if you have loads of children you only parent a few and shouldn't have them as you are getting your older ones to raise most of your children for you.
BTW, I don't actually think that about only children as I'm not small minded enough to put people into boxes and make sweeping generalisations.