Waterproof Cover - Arm Cover For Adults - Arm Use Please check the size in photo 7. Hole diameter: approximately 5cm. Since it's 5cm when not expanded, it's large enough for children, unless they are preschoolers or have very thin arms. I purchased a leg cover online, but the arm cover arrived by mistake, so I'm selling it since I won't be using it. I opened the bag and unfolded the product, but immediately put it back in the bag. Plaster Cast Waterproof Cover Silicone Plaster Cast Cover Hand Foot Adult Child Fracture Shower Cover Reusable Plaster Cast Cover Waterproof Shower Bandage Cover Washable Clean Soft Bandage Cover (For Children, Foot)