Flash Muscle Costume - Child Costume - Small (4-6) . $36.88. Flash Muscle Costume includes: red character muscle chest jumpsuit (button closure in the back) with attached boot covers, yellow belt and character headpiece. Product is available in Toddler size (2-4) for 1 to 2 years old, and Medium size (8-10) for 5 to 7 years old. Made of 100% polyester. Care instructions: hand wash in cold water, line dry, do not bleach.