Writing experts suggest to authors of children’s literature the following technique for finding their voice:
a. observe the people around you and try to create interesting story scenarios in which they are the characters.
b. read the best in children’s literature, both past and present.
c. give one of your main character a foreign accent or an american dialect (a southern drawl, for instance).
d. get in touch with your ideal, imaginary reader.

No matter what kind of writing you will do, it begins with reading. You must read deeply and widely in the type of writing you would like to do. Schooling is good too. Learning the various conventions of that writing genre, working with a teacher or a mentor. But you can't even function at that level without first having read a good deal of the writing in question. 

Now, I would say that to find your *voice,* you must also write. Only in the practice of writing can you really learn what works — for you.

Looking at those four responses, I think you can toss out C and D pretty quickly. But — which is the better avenue for finding your voice, writing up scenarios for practice or reading the best that this genre has to offer. That's a tough one. I would say the would-be writer should do B first (wide reading) and then some version of A (writing). 

But to find your voice, you must practice. So . . . it must be A. (Not that that's the only way to go about practicing writing, but it would be an easy way to get started.)