Pattern is only available in German at the moment.
It’s a generic pattern that gives instructions how to calculate from gauge and foot measurements the number of stitches needed. Choose any yarn between fingering and aran and needles that give you the fabric you like. Knit a little piece in garter stitch, get you stitch count and off you go.
Because of being in garter stitch they are very stretchy and fit for a rather long time. The cord gives them enough grip to stay on a babys foot.
I made those in different yarns for my children until they started walking around.