I found a simple toddler vest pattern (FREE), but did one fancier cable in the middle instead of two simpler cables on the sides that the pattern called for. The back is plain stockinette. I also did 2 x 2 ribbing instead of 1 x 1 ribbing. I picked up stitches and added the neck and armpit ribbing after the rest of the vest was complete and sewn together. It was an easy knit and went quickly with worsted weight yarn and size 8 needles.
J's Cabled Christmas Vest
Pattern: My own (Adapted from Lion Brand Free Knitting Pattern Cable Vest)
Cable pattern: Braided Cable from Vogue Dictionary of Knitted Stitches
Yarn: 2 skeins of Plymouth Encore (25% Wool/75% Acrylic) (1 skein=100g/3.5 oz/200yards)
Needles: Size 8
Vest size: 3 years/26 in. chest (pattern includes 6 months, 1 year, 2 years, 3 years, 4 years)
Gauge: 17 st x 24 rows = 4 inches in stockinette stitch