This pattern is available in various guages, depending on your yarn weight, needles, and child’s size - just swatch and choose from the following patterns using the guage.

boatneck sweater
childrens sweaters 16 x 22 (sts x rows per 4in/10cm)
childrens sweaters 18 x 24
childrens sweaters 20 x 26
childrens sweaters 22 x 30
childrens sweaters 24 x 32
childrens sweaters 26 x 34