I dont think we should expect for the child to provide for us, in this day and age. Having kid(s) is a huge responsibility and parenting needs to right. People who are up for this challenge should have kids. If in doubt have only 1 kid or 0 kids to minimize risk. For example, having 1 badly broughtup kid is better than having 3 badly brought up kids, lol.
After parenting is done right, then at the max we can expect our kid(s) to be there for us for emotional support at old age. Not really financial support. We should make sure we have plenty of wealth. But even with all the wealth in the old age, if you have to rely on the goodwill of strangers, then that is a bit of risk.
The ideal scenario is where you make plenty of wealth and you do proper upbringining so that kids are there to take care of you because it is right thing to do, and not because of some obligation or for inheritance.
It is a very tough challenge and luck plays a big part too.