Measurements: The 6 months size has a finished chest measurement of 20 inches, the 12 month size is 22 inches finished, and the 24 month size is 25 inches finished. The 6 months size is meant to fit a 17 inch chest, the 12 month size fits a 18 inch chest, and the 24 month size fits a 20 inch chest.
Suggested Yarn: The 6 month size calls for 5 ounces, the 12 months size for 5.5 ounces, and the 24 months size for 6.5 ounces. The skeins of the Red Heart Strata yarn differ in their amount of yardage (192-222 yards in 4 ounces according to the Ravelry entry) depending upon the color you select; however, since none of the sizes require a full two skeins of yarn this should not be a problem on this pattern if you use the suggested yarn.
Substitute Yarns: If you choose not to use the suggested yarn, the yardage calculations above used 222 yards in 4 ounces to compensate for the variation in yardage of the suggested yarn. This works out to 55.5 yards per ounce.
Additional Materials: The pattern calls for a yarn needle, stitch holders, and a stitch marker.