It just so happens that your kids do not love sports, so they don't really root for a team. What I'm trying to get across here is that when father and son both enjoy sports, they tend to root for the same teams. When one chooses which teams to root for, there's 3 factors:
1) Root for dad's (or close family member's) team since basically birth.
2) Geographic location. This often coincides with dad's team, since in most instances father and son live in the same household or in close proximity. If you grow up in Chicago, you're gonna be a Bears, Bulls and Blackhawks fan, and Cubs or Sox. There's the occasional oddball kid who likes an out-of-town team for whatever reason, maybe because their logo appeals to them or one specific player. But the vast majority of kids and dads root for the local team.
3) Association. If you or a family member or close friend somehow become associated with a team or university, you are likely to root for that team. If you grew up in Boston and attended The U, then you will root for the U. And so will your dad. If your mom lands an accounting job with the Pittsburgh Penguins, you will tend to root for them as well although it won't consume you like your love for the U.
All I'm trying to say is that when father and son/daughter both love sports, they will root for the same teams way more often than not.