Having a child is an informed choice; it's by all objective means a hugely unfair deal yet many people are opting into it for emotional (or hormonal) reasons. Not because they want to materially slave for their kids however, but because they love them and/or want to leave a legacy.

You chose to bring a child into this world. They owe you absolutely nothing for it. They'll help you if they feel love and/or obligation for you, just like I will keep supporting my widowed mother until her death.

But this shouldn't be expected by default -- or legally enforced. It should be a choice. We pay enough taxes as it is, surely the politicians can spare some change to care for our elders.