Gap takes up to 40% off during its Kids & Baby Sale. That's tied with our September mention as the best sale we've seen specifically on these items in nearly a year. Shipping adds $7, or spend $50 or more to qualify for free shipping. Some exclusions apply and sales tax is added where applicable. Sale ends March 2.
A best bet is the Gap Girls' Floral Ruffle Romper (pictured) for $22.46 plus $7 for shipping. That's $8 off and the lowest total price we've seen for a Gap romper. It's available in sizes 12-18M to 5Y.