The reason that the parks are geared towards retirees is that most kids are in school during the winter not sitting by the pool in the SW desert. Most people with kids RV during their vacations at places like state/national parks where there are a lot of outdoor things to do. There is a palm tree on our lot here i Mesa, surrounded by typical desert landscape. The southwest has been in a drought for the past few years, the only green areas will be golf courses willing to pay for the water (usually treated waste water) to keep them green.
I think you have very unreal expectations of what you will find in terms of children's activies in the winter. BTW - you really think about having a car - would make your life so much easier.