Sorry Oz, you know I adore you but I'm gonna' fling the bullshit flag out onto the field on this one. I'm groovy with poly when it does indeed work for all parties involved, I've said as much prior in the thread. It's all about what you can handle and not biting off more than you can chew. However, a parent to child relationship and a sibling to sibling relationship is not the same dynamic as romantic and sexual love between adults. A parent raising a child is mentoring a growing person with a developing intellect into a young adult who will one day be outed from the nest and expected to exist on their own. As parents, part of the job description is to make the little snot nosed DNA copies function apart from us. As romantic partners (key word there being "partner") the goal is the opposite: we're trying to figure out how to function with each other.
A parent, I would hope, would indeed love their child/ren for life. I would hope a parent would not choose obvious favorites. My parents had three of us, loved us all and cared for us all and their pride and love is clear in their eyes when they look at each one of us. However, it is nothing compared to the depth that exists when they look at each other and, in their case, only each other. After nearly 33 years of marriage they are still so enthralled with each other that there is simply no more room for anyone else.