How does Extend Size work?
Some of our children's waterproof nylon and polyester garments have Extend Size, which lets you lengthen the sleeves and legs by roughly one size as your child grows.
Look for the specially marked red seams inside the sleeve and leg lining. Carefully unpick these seams with a seam ripper, taking care not to damage the fabric.
Check the product description to see whether your garment has Extend Size.