The darker side to childlessness and why you can't just "pay off" your future with money: 40% of aged care residents face abuse
Family check-ups in aged care ensure that abuse or neglect is noticed early and investigated. If you have no children checking up on you, why would the abuse or neglect stop?
Most aged care workers are low skilled foreigners. There is no incentive for those workers to do their jobs properly.
Obviously not all children are going to take care of their parents, but if you have 3+ kids, chances are at least one will be a "home body" type who will do a bit more than the others. My observation is that larger families that are close-nit tend to have carer roles shared, even if one child instinctively does more than the others.
I've heard some horrendous anecdotal examples of childless older people being tied to beds, starved of food and having nappies left on for too long. It is easy to assume you'll just 'pay off' the problem down the line, but you'll be joined with other folks doing the same, driving prices through the roof.