There are different styles of this unicorn floatie, which comes as an accessory for bathtime baby dolls. Some of the store brands they are marketed under are My Sweet Love (at Wal-mart) and Dream Collection. They measure about 10″ long, and I’ve found two different styles.
Note that this one has the same style as a couple generations ago of Wonder Pony Land:
This one has different eyes, different mane style, and molded wings:
