I hate to sound like some sort of parrot but I agree. She looks so at home in the role!
And other roles where she's been a Mum. The end of Satan School For Girls for example. And playing with baby Matthew in the Charmed episode Reckless Abandon. Or even playing Aunt Cate in Christmas Caper.
Shes gonna be a wonderful Mum someday!
It's not just her a kids though. I was watching Astral Monkey (again, seen it so many times and still love it!) and Shannen looks adorable with "Prue Monkey" too.
I found a wonderful photo of her posing with it on the set. I think Shannen is just lovely with the monkey and lovely with kids. She has a nurturing personality.
http://innocently-charmed.com/gallery/displayimage.php?album=287&pos=5
I know that should probably go in the Charmed suite but it's relevant to this discussion!