All models are begun at the sole.
The sole is knitted the same for all booties.
The pattern is for 4 sizes.
The smallest is for newborn, for which the sole is 8 to 9cm long.
We start with the sole in rounds.

st(s) = stitch(es)
p = purl
yo = yarn over
k2tog = knit 2 stitches together
sl1, k1, psso = slip 1, k 1, pass the slipped stitch over the knitted stitch

0 to 6 months
6 to 9 months
9 to 12 months
12 to 15 months

Ca. 30g baby wool or any other yarn for 3 mm needles
Double pointed needles 2.5 or 3 mm