Walmart has Lego Batman Boys One Piece Hooded Costume Union Suit Pajama, Sizes 4-12 for $8.00. Shipping is free w/ Walmart+ ( free trial available ) on orders $35+
Product Description from Store
Officially Licensed: Made in collaboration with your favorite franchises, your little will love these PJs featuring authentic art and characters. Unionsuit Design: This new take on the classic onesie delivers everything they need in one single piece. Material: Made with lightweight polyester jersey to keep them comfortable and cool during the night. Safety: Treated for fire resistance to meet safety standards. Care: All pieces are machine washable and safe to tumble dry.