For me, I see poly as not about choosing. For example, say you did go out with a hot, young blonde. You go back to your gf because you liove her for who she is. It has nothing to do with how you feel about the blonde. In other words, you two are together because you like each other (for whatever reason) and not because you are stuck with her or because she is the perfect person in the world.
In a monogamous view, people want the best person they can get. They have to be the best in all fields. They have to be the most attractive, funniest, entertaining, secure, etc person you can possible get. if someone better comes along than who you are with, it seems to be in your best interest to grab that person instead.
In a poly view, be with someone because you like something about them, not because they ranked high everywhere. And your girlfriend is special to you because you keep going back to her. That shows that you do value her. (Plus it doesn't hurt to tell her what you really like about her.)
As for kids, they do fine in poly relationships. For the most part, kids adapt well as long as you do not portray it was immoral. You don't have to give specifics of a relationship, but showing love for several people only looks unnatural if you grew up not seeing it.