This is a pattern for a girl’s tunic using 2 yarns, alternating 2 rows of garter stitch in each. The instructions are for sizes from 2 years (104 cm chest) to 12 years (152 cm chest), and uses 2 balls of each yarn for the smallest, up to 4 balls of each for the largest size.
The gauge shown above is for the main pattern using no. 5 needles - the smaller needles are only used for the neckline.