I'm a parent, they'll never be anything more important in your life than your kids, but Brady's kids are 15, 13 & 10 and their entire lives he's been a professional athlete. It's what they're all familiar with and it's afforded them many life advantages.
I really think Brady is retiring because he's coming off a disappointing season, and at age 46, he doesn't think he'll have the competitive drive to commit to the full process of being an NFL quarterback anymore. With his obsessive nature, he's at it year round, conditioning, rehab, film study, etc... it's part of what made him so great for so long. But being that way, it's exhausting, so he's trying to step out of it. Unfortunately for him, his nature being what it is, he'll probably obsess now about other things in his life.