Seems like I stirred things up a bit there!
I agree that, in principle, people with kids may spend more than those without, all other things being equal. That being so perhaps we should have preferential parking for people driving cars under 2 years old, or who got paid in the last 2 days, or who have a Gold credit card. A new use for Reward Points perhaps. ;-)
I go back to the fact that people are not forced to have children. It is a choice, balancing factors including the knowledge they they may have to do the sort of things that you describe so eloquently, in exchange for other, more pleasurable experiences. Without trying to cause offence, if someone's sole motive for having children were to continue the human race then they are a highly admirable and selfless, if somewhat misguided, person.
On the topic in hand, it would be a tragedy indeed if all disabled spaces were full, and an old woman with a zimmer frame had to park at the far end of the car park, because she didn't have a small child!
Smithers, please accept this response in the spirit in which it is intended. It is my slightly exaggerated, tongue in cheek opinion as part of a lively debate, and not a personal attack on you or any other people with children!