LEGO does a great job of making it easy to find replacement parts for your sets. (They even have age-appropriate forms to provide more help to kids.) The response to filling out the form:
Thank you for emailing LEGO Consumer Services. We were disappointed to hear that your new LEGO set contained a faulty part. We work really hard to make sure that our products meet your expectations of the LEGO Group so we’re sorry that this wasn’t the case with your recent experience. Unless we need to contact you regarding your part, we’ll send a replacement to you as quickly as possible. This should arrive within 10 business days.
Too bad it takes 10 business days from the parts to arrive. That’s an eternity to a kid with a brand-new LEGO set.
Same-day fulfillment wouldn’t be hard. It’s the same item being sent by the same labor at the same cost. It would just take better planning and management. (Maybe they can outsource the shipping to Zappos …)