The yarns showcased here are generally classified as DK (double knit) weight, which is lighter that worsted and heavier than sport weight. DK weight yarns are popular in light weight garments and baby patterns.
Remember that some yarns don't fall neatly into a category, so some categorized as slightly smaller or slightly larger may also meet your needs! Want more information about yarn weights? Check out this page from the Craft Yarn Council!