All the pieces of this set are knit using a tubular slip stitch pattern. They could be knit flat and seamed on a standard gauge single bed machine with patterning, if you relatch stitches for the ribbed areas. Since measurements are on the schmatics, a few calculations would allow knitting plain versions on any gauge machine.

The hat is especially cute, and the method solves the issue of decreases at the crown by knitting straight then gathering the fabric between the second and third pattern repeats to make a ruffled top, which if further improved by a tie with pompom ends.