Munchkinmuffs may be a good idea because on occasion there are times kids are exposed to loud noises. Are they exposed often enough to purchase muffs? I'm not sure. No baby belongs at an NBA game, just as no child belongs in a bar, a casino, a rock concert (that's not outside) or anyplace exceedingly loud. Now would parents buy muffs for trying to get them to sleep in loud places? Yes. too often I've tried getting my kids to sleep in noisy places and muffs that are soft and can be slept on would be a big seller. Examples of places to use them: Camping, airplanes, airports, hotels, staying with friends or family, or having guests stay at your home. My 7yo just did a camp out at the Museum of Science with scouts. He would have slept a bit more with muffs!
Just food for thought. When starting a new business, keep an open mind, the product idea you start out with may be a very different one you actually launch. Get as much feedback as possible and perhaps do a forum or two.
Dana