I bought size M (10/12) and ended up using them for my youngest son as they run small. He is 7 years old, 49 inches tall and weighs about 55 pounds. His waist measurement is about 23 inches. Medium Jammer is expectedly narrow, but will outgrow this size within a year. By that point, he'll likely inherit his big brother's XL mufflers, which are barely larger than M. When flat, the M-Mufflers are 10 inches wide at the waist, with an overall length of 13 inches and an inseam of about 7 inches. .My eldest son can still wear the large XL mufflers for a few months although he complains that they are too tight. He is 9 years old, 57 inches tall and weighs 80 pounds. His waist measurement is about 26 inches. When laid flat, the XL Jammers are 11" wide at the waist, 15" overall length and 9" inseam. They hold up to a weekly wash, although I line dry them. This is a good deal for the price.
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