Kids books are a really tough sell at the best of times, and there is fierce completion from not only other self-pubbed authors, but the big, well-known names as well.
My first look at your books told me everything I needed to know... your covers! Well, they're not exactly going to grab a five year old's attention, are they?
I don't mean to be rude, but they would be more suited to an academic text-book than a children's book.
I glanced at a couple of your stories in your Look Inside, and they seemed quite sweet and appropriate for the age-bracket. But unless you can attract a customer to actually look inside, nobody is ever going to know that.
Invest in some better covers and your books will stand a better chance.
Probably the best step for you at this point is to click on the subgenres under which your books appear. That will take you to the Top Hundred list. You'll see that they all have attractive, age-appropriate, professional covers. None of them have blurbs that sound like dry catalog listings. And you'll find the contents well formatted and written in such a way as to engage the child. You might also consider whether customers would really think paying any amount for less than a dozen pages is a good deal.
Even if you improve your product to the point where it competes on a equal footing with the other books, it will still be an uphill battle. As already mentioned, competition is stiff and sales are low for all but the lucky or well-known few. Despite Amazon's best efforts to create a kiddie e-book market, it's still a black hole into which unknown writers throw massive amounts of time and money without any real return of investment. If high sales is an important goal, I can't imagine anyone getting into the field...print books, perhaps, but not e-books. Good luck.