I had a moment -- which I may have already told you about -- when I realized I had completely crossed the line from identifying as a member of the younger generation, to being A Mom. Lizzie and Mona were probably about 5 and 6, and I took them to see the Big Apple Circus. There was a wonderful trapeze artist -- a young woman in her 20s -- scantily dressed, with sequins and fringe, doing amazing feats, including hanging by her heels on a very high trapeze. She was great, the girls were rapt, and the thought which came screaming into my mind was, "Does her mother know she's doing this?!?!?"
The basic mother-reaction is what gets us evicted from a lot of children's literature. A good deal of growing up has to do with learning how to interact with the world without the intervening presence of a parent. That includes everything from learning to handle a spoon and bring the pablum to your mouth, as I suspect your Isabel is by now pretty good at, to driving hundreds of miles on your own on big highways, as both Lizzie and Mona did (separately) for the first time this year. And so much in between and beyond. Many of the interesting events in children's literature have to do with gaining skills and knowledge without your parents handing you that knowledge. Babar going into the big city, James ending up in the giant peach, Pippi living without limits, Jim Hawkins facing Long John Silver, Sara Crewe discovering her inner strengths, Stuart searching for Margalo, the Cat in the Hat wreaking havoc -- none of this stuff happens if Mom's there too. Sure, there are great books with wonderful parents in them too. (I keep coming back to the Ramona books by Beverly Cleary: the parents have their own lives and personalities, and their own separate relationships with their daughters.) But removing parental supervision is a tried and true way to get a story going.
It helps to see the dead/absent/ignored mother as a plot device, a door to the imagination, and not as a real desire. At different points in any child's life, a story with a dead mother can be a very scary event, or just part of the set-up to a good yarn -- as you point out, one's choice of reading material is always specific to one's child. The parent gets to offer the variety of creative escapes, while still providing the basic security from which a child can venture into the world.
I think my next post will talk about some wonderful parents in children's lit...