The nature of love within the brain is discussed here as well.
It's a very interesting point of view made by anthropologist Helen Fisher
At 1730 she does state that you can be in love with more than one person. She attributes this to the three brain systems, Lust, Romantic Love and Attachment. She points out that they are not always in sync but that they can be too. She says you can have Attachment for one while having Romantic Love for another. She doesn’t say you can have Attachment for more than one though..what message does this really imply? Does this mean she doesn’t think you can have all three for more than one person?
Her talk was about adult bonding relationships..not sibling or parental love just to clarify. I would think the Romantic and Lust sections would not be engaged for children within a normal adult.
I've e-mailed her directly for some clarification and hopefully will get a response.
I used to use the "you can love more than one child" argument at one time too. I dropped it once I conceded that the kind of love people were talking about was the kind that made you want to fuck the object of that love. That kind of blatantly pointed out a different type of love which I was personally not comfortable directing towards any child.