Is using Amazon's advertising for a children's ebook effective?

Yes; if you do a presale, those buyers will get the book immediately upon release. Include a message in either the front or back matter that encourages them to leave a review once they finish the book. You should also encounter them to join your mailing list, that way you can continue to build a relationship with them.

Basically, the question is this: Are people reading the book for your writing, or for your ideas? If it's for your writing (say, if you're a fiction author) then you should probably write it yourself. It'd be disingenuous not to. If they're interested in your ideas (which is the case with most Kindle non-fiction books), then what's important is that your ideas aren't lost. That doesn't mean ghostwriting is fine, only that you need to find an efficient way to get your ideas out without wasting your time writing. Basically, the process I use is to outline the book myself, sit down with a microphone, and talk through the entire book (basically recording a really rough draft of the audiobook straight from the outline). Then I transcribe it, and then hire a "writer" to work from the transcription to the finished text. That way it's high quality and maintains my ideas, but I don't have to do all the work of typing. I wrote a book that breaks down the process in a bit more detail (especially the process of outlining, how to record effectively, how to find that editor, etc.), but basically what I said above is all you really need to know. Here's the link if you want to check it out: www.amazon.com/Book-Box-Method-Quickly-Easily-ebook/dp/B014EUTYGM/

If you sign up with KDP select, you'll be given 5 days where you can drop the price to free. You'll be restricted to only publish on their platform, however. Hit up your email list, use sites like BookBub, or reddit.com/r/FreeEBooks in order to prepare for the discount launch. Start the deal on a Sunday since more people will be at home and prepared to read rather than Friday and Saturday nights when they're out. Include, at the end of your book, a request for people to leave honest feedback. They're more apt to do it if you remind them. You can also include links to your other titles. I've published a handful of titles under different pen names but I'm not an expert. I just figured I'd share what my research picked up.

Obviously you need to generate more leads. But then you need to segment your list. Your basic list are those leads who "come aboard" and want to know what's going on. Your qualified leads list are your potential buyers. Between the two, you need a gate. So, they come on your big list. Then they need to get something that qualifies them from being a basic prospect to being a qualified prospect. That puts them on the second list. Leads >> Qualifier >> Qualified Leads. What's the topic of your book? Qualify by things people have said in similar book reviews. This is a lot easier if you are doing non-fiction, but it's possible with fiction as well. In the reviews you'll see people saying things like, "I bought this book because..." What they say after that is the pain point. Use this language, as they wrote it, in your qualifier. For example, in a review for SPIN Selling, someone says, " I don't do "hit and run," one-time sales. Tom Hopkins and Zig Ziglar offer great tactics for those kind of salespeople, but they don't work for me." Another says, "...I had no idea how to sell professionally. I had already read a few books by Tom Hopkins, but felt he was targeting used-car salesmen types. It seems as though Hopkins' techniques relied on "closing" gimmicks when it came down to it. (I must say I did learn some good principles from Hopkins, but his gimmicky style is not for me.) I was instantly attracted to SPIN SELLING when I saw that (1) it was based on extensive research, and (2) it dealt primarily with the large sale. Since I want to start my own corporation after my MBA, and want to have Fortune-500 companies as my customers, I realized SPIN SELLING was for me." See the commonality? So if I was launching a solid B2B sales techniques book, I would make use of this language. First, I would attract them to my basic list with the promise of a corporate B2B sales book. Then, I would qualify further with language like, "Are you looking to build real relationships with your customers, instead of hit-and-run one-time sales tricks? Are you eager to understand the secrets of professional corporate selling?" A Call To Action would follow. Those who respond to this language are qualified leads, as salespeople in other situations would not resonate with that copy. How can you transfer what I've shown you here to your niche? If you're writing non-fiction, as I said, it should be straightforward. If it's fiction, then you can find similar stories and pull from the reviews for those...the things they say they like about the author's style (assuming yours is like theirs), the story structure, the excitement, the thought process, or whatever. Why not just go straight for the qualified leads? Because your net won't be big enough. Better to grab a whole lot of interested readers, which you can make use of later as well, and qualify from there.

Not any way that I can think of. I would trust Amazon's judgement on this one. They want to sell your book just as much as you do.