If you are handy with a glue gun and would prefer to make your own costume for Halloween this year, this DIY unicorn Halloween costume could be the perfect fit.
From Mashable, the project requires an old hoodie, poster board and gold fabric for the horn, felt for the ears and fabric in assorted colors for the mane and tail. You have a lot of wiggle room in terms of color scheme and fabric variety. Mashable's example mostly stuck with felt in rainbow colors and matched the ears to the hoodie color. You could alternatively go with an all white look for your own unicorn Halloween costume.
This can easily be replicated for children, as long as you have a tiny hooded sweatshirt or similar garment.