Kids are expensive and require a lot of time of an adult's available time.
Extra money and time are required to explore green / lifestyle changes, and you usually have less available when you have kids.

For example, here are a couple of decisions I have to make frequently:

"If I spend an extra two hours today to commute by bike instead of drive, will I have time to help my kid with their homework?".
"Do I want to spend $1,000 dollars on a bike or new gadget, or do I wan't to save it to send my kids to college?"
"Do I want to spend 6 - 8 hours today riding a century, or do I want to spend the time playing with the family?"

For the typical person, family occupies the second and third area in Maslow's Hierarchy of needs, (Safety and Love/Belonging), both of which are higher priority then Problem Solving and Acceptance of facts, which is considered lowest priority on the hierarchy. Family will usually win out everytime.