After some feedback via Ravelry, I’ve reworded the heel flap instruction, please let me know (either over there or on here) if this makes it clearer!
I made three pairs of socks in the three sizes below, using the tiniest amount of yarn possible, including some leftover from a pair his mum had made herself so now they have matching socks!
Using 4ply sock yarn and 2.5 mm needles
CO 28 (32,36)sts, join in the round
k1, p1 for 4(6,6) rows
knit until desired leg length (about 5cm)
This is worked over half of the stitches (the remainder will stay on their respective needles and be reintroduced later)
K14 (16, 18) sts, turn and purl to the end of these 14 (16, 18) stitches
(I have used an Eye of Partridge heel stitch)
Row 1: *Sl1, k1* repeat until last st – ktbl
Row 2: *Sl1 purlwise, p* repeat to end
Row 3: Sl2, *k1, sl1* repeat to last st – ktbl
Row 4: *Sl1 purlwise, p* repeat to end
Repeat these 4 rows 3 (3.5, 4) times until there are 14 (16, 18) rows altogether in the heel flap (including the first 2 set up rows)
Row 1: Knit 9 (11,13) sts, turn
Row 2: Purl 3(5,7),p2tog, p1, turn
Next row: Knit to one st before the gap, ssk, k1, turn
Next row: Purl to one st before the gap, p2tog, p1, turn
Continue until all sts knitted – 8 (10, 12) sts should remain on the heel.
Pick up and knit 14 (16,18) sts along right gusset, place marker, knit the 14 (16,18) sts across top of sock, place marker, pick up and knit 14 (16,18) sts along right gusset and remaining heel sts. Total of 50 (58, 64) sts left
Next round: k to last 3 sts before marker, k2tog, k1, knit until next marker, k1,ssk then knit until end of round.
2nd round: knit every st
Repeat these 2 rounds until 14 (16,18) sts remain on the foot. 28 (32,36) sts in total
Continue until foot desired length – only a few more rounds as babies feet are so tiny, this is more of a judgement call than a precise number of rows!
Ensure sts are evenly spread across the needles and in the centre of the sock.
Needle 1: (right side, bottom of sock): k1, ssk, knit to end of needle
Needle 2: (left side, bottom of sock): knit to last 3, k2tog, k1
Needle 3: (right side, top of sock): k1, ssk, knit to end of needle
Needle 4: (left side,top of sock): k to last 3 sts, k2tog, k1.
Next 2 rounds: knit all stitches.
Repeat these three rounds until 12 (14,16) sts remaining – should end up with 6 sts on front needle and 6 on back needle – use kitchener stitch to finish.