There was perhaps a time when I would have tutted, but my best friend has 4 kids by three different fathers and it would be easy to dismiss her as irresponsible. But when you learn that the father of her eldest did a runner the minute he knew she was pregnant (she was 16) and her mother threw her out, the father of the second rejected the eldest outright and the father of her two youngest ran her into debt before leaving her for another woman and rendering her effectively homeless, then it's clear she's doing her best under very difficult cricumstances.
For all that, I cannot fault her ability as a parent, nor the behaviour of her kids (they're a lovely bunch). She and her kids are thoughtful, respectful, self-respecting and well-mannered and she is rightfully proud of them.
I also knew an Irish Catholic family with 7 kids. Easy to turn your nose up at them, but best not to, because the parents were both GPs, the kids were all very talented musicians and the family hadn't claimed so much as a penny in benefits. The Mum said she wouldn't have had them if she had thought for a minute she couldn't raise them properly.
So tell the next person, when they adopt this attitude, "Yeah, five. Bet you wish you were as lucky/clever as me!"