All our DK and light worsted weight yarns. These are great for baby items and lightweight garments. Generally about 22 sts on US 3-5. The "light worsted" are those that are just a little thinner than your average worsted weight.
Yarns come in all kinds of thicknesses, from lace weight to jumbo. Generally the thinner the yarn, the smaller the needle or hook size you use. Conversely, the thicker the yarn, the bigger the tool size you use. But, of course, you can often use a different tool size than recommended - not only to obtain gauge, but to create a different kind of fabric - drapier or firmer, depending on your desire.
Find a chart of the standard yarn weights here.