Is it too fast?

It's fine, especially for a first draft. After you finish your book-embryo, you can go back and add more stuff if you feel you need to. But generally, you start the book at the inciting incident. I suspect that being a five-year-old isn't all that interesting, so you may wind up cutting even this in future drafts, and only put in the mother's death when it's important to the "now" of the story.

But for a first draft, go ahead and put it in. The important thing is to get started, and keep writing. BTW, don't feel you have to write in order, either. Modern technology makes it extremely easy to go back and insert more text, or cut-and-paste passages to the right part of the book.

I'd say you probably know it's a little too short, otherwise you wouldn't ask the question. But I'd have to read the book to say whether that is true. There's no telling. If its integral to the plot, you might fair well making your book a short story or a novella.

Typically, a writer has a few landmarks in their lives.

1. The writer writes their first short story. This is the fundamental most important step in a young writer's career. The reason why is because it teaches the writer how to finish a story, and structure a story, and understand the basic mechanics of storytelling. So, this is why I suggest you make it a short story. If you're asking this question, you haven't much experience, so you should probably get the fundamental element of plot down before you go any further.

2. The second stage in a writer's life is writing a book. A writer's first book attempt is probably not going to survive more than a few years, but like short stories, a book is something that has to be worked up to. You have to understand the fact that you have more time to develop things, and often that's what's expected of you. Your first novel is a huge landmark in your career because you finally wrote a lot of words, and you made them make sense.

3. A writer's third step is learning how to self edit proficiently. This is the most often ignored step, but it is the most helpful. A writer should be a master of grammar. If they are, they won't be messed with during the editorial process, and they'll have a book that was primarily written by their hand.

4. A writer's fourth step is copyrighting. This is how you own your piece of writing.

5. A writer's fifth step, if you ever get this far, is having other people read your work to get feedback. This is important because it helps you hone your craft. A good piece of advice for this step is, "Don't listen to advice unless it is something technical about your story which could hinder the way it is understood."

6. Your sixth and final step as a writer is publication. This can be done numerous ways, and you should be researching it throughout the writing process how you'd like to get your book out there. This way it gives you a goal.

These goals are not solitary goals. They should all be worked on at the same time. Just, the order I have them written is the ideal order you should achieve these goals. I still have my first completed short story, and it's, well, it's not very good, but it educated me on the basic mechanic of storytelling. Try that first, and then work your way up to novels.

If you are killing off a principal character so soon, why include her at all unless to play up the child's trauma? If you do not want trauma, reexamine the need to kill the mother.

yes