Changing Hair
A: As we grow our bodies change, usually according to our genetic blueprint. A child who has fine, sparse hair at the age of two may have denser, thicker hair by the time he is five.
To give an example: My cousin had a head full of silky curls when she was a baby and toddler. My grandmother had advised my aunt to keep my cousin's hair trimmed - specifically to trim off the longer, straighter locks that began to grow. She believed that by keeping the straight hair trimmed the hair would stay curly.
Of course, it didn't. The hair grew longer, thicker, and the weight alone loosened much of the curl. By the time she started first grade, her hair was more wavy than curly, and now as an adult it is a lush, full head of soft wavy hair.
The reason your granddaughter's hair spirals at the ends but is only wavy closer to the scalp is partly because of the weight of the hair pulling out the curl, and partly due to the gradual shift in the way the hair grows as the follicles mature.
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See also:
Hair growth Q&A
Hair wave pattern
Curly hair and hairstyles
Change in hair texture because of genetics, environment or products