I agree with what was said before. A lot of great thing in your work! But what I think is missing is story... currently they look more like pieces you would hang in a kids bedroom (which is not a bad thing!) but not really something you would see in a kid book. I think part of the "problem" is also the foliage all around the image, makes it look more like a decorative piece then an illustration you would see in a book. For your next serie (I love the underwater idea!) try maybe coming up with a simple story to illustrate! Story in always the key in illustration!
Also, I think it would be a good idea to ALSO do digital - However, it is not necessarily easier. And I would give up acrylics, I think is looks great! One way you can use digital to make your life easier without giving up acrylics is to sketch digitally (I find the undo button and transform tool SO helpful for sketching!! But then color in acrylics :)
Hope this helps!