I don't think that is true. It is all about what is a priority. I have 3 kids plus another on the way, a day job, and multiple side projects/products (one being Hacker Newsletter). My family is my priority, so it is very rare for me to work on the side projects while the kids are awake. You just have to cut things that aren't as meaningful to you. For me that was TV/Facebook/etc. I also think it is good to mix-up what you work on. Some weeks I'll spend a minimal amount of time on my side-projects and instead do some wood working projects or what have you.