This was done as a animal pillow for my granddaughter. She loves carrying her stuffed animals around with her and especially when she goes on a trip and falls asleep in the car.
Different yarns and different weights will cause your pillow to either be smaller or larger.
I do not suggest this pattern for a child younger than 4 or 5 as any younger and they might pull the batting from between the stitches.
Gauge is not important.
The size of your pillow will be determined by the yarn weight and hook size. Be sure to use the smallest hook available for your yarn (about 1 to 2 sizes smaller than suggested).