The plastic tampon applicator that is found on a beach after a high tide or a storm surge.
Normally found by children who play in the sand. To save embarrassment or an in-depth conversation with a 3 year old you simply dismiss the buried treasure by non-chalantly saying "Oh honey, you just found a sea whistle!" Then you blow into the top of it to make a sound. You and your children will laugh for hours!!
For added fun you can send the kids on a sea whistle treasure hunt!! gather enough sea whistles and you can sting them together and make a necklace!