This sweater is knit from the bottom up in 4 pieces. The back, front and 2 sleeves.
A simple 11 stitch lace pattern repeat is followed for the front and back pieces from the bottom up to the neck where it is shaped and then bound off. The sleeves are knit from the cuff to the shoulder where a purl ridge is knit to attach the ruffle before being bound off.
The ruffle is a simple knit in stockinette.
The pieces are sewn together using mattress stitch and the collar is picked up and knit in the round with a rib stitch.

Sizes:
3mths (6mths, 1yr, 2yr, 4yr, 6yr)

Yarn
Rico, essentials merino DK yarn (100% merino, 120m per 50g ball)
This yarn balls listed below are based on yarn with 120m/132 yards per 50g ball.
4 (4, 5, 5, 7, 8) balls or 377 (412, 506, 593, 774, 930) metres/ 413 (451, 554, 649, 846, 1,017) yards. This includes enough yarn to make a 20x20cm swatch.
If your chosen yarn has lesser yardage, you will need to purchase more balls of yarn. The sweater pictured above was knit with Rico Essentials Merino (DK) in colour Mauve (20).

Needles
3.25mm (US 3) knitting needles
4mm (US 6) knitting needles

Tension after blocking
23 sts and 31 rows to 10cm/4in square in st st using 4mm (US 6) needles. It is more important to get the stitch gauge correct rather than rows as this pattern will tell you the length to knit to.

Notations
BOR marker
Stitch markers for pattern repeats
Tapestry needle to weave in ends
2 x 15mm Buttons