I followed the pattern until I had done four sets of seed stitch rows (eight rows) then did one row knit, one row purl, then added the four rows of seed stitch I didn’t do as stockinette to the eight knit rows after that. This was in the interest of time as I am slow on seed stitch and I don’t think the baby will notice my seed stitch efforts.

Adapted the pattern to fit my 2.5-kilo newborn as the small is too big on him:
CO 72 on 4mm (don’t join)
Rows 1-10: K2, P2 ribbing (still not joined)
Join in the round
Knit stockinette for 30 rows
Place half stitches on stitch holder to knit one leg
Each leg: Knit stockinette for 40 rows
Bind off