The charity's website describes the badge, on sale from the site for £19, as "a small device using the latest technology to repel head lice from infesting children and adults".
"It is in the form of a badge of the unicorn and is pinned to the clothing of the individual," the website says. "Its effect on head lice is to repel them."
In response to a complaint about the website, the ASA asked the charity, which is based in Wincanton, Somerset, to provide evidence to support its claim.
The ASA's report, published today, says the charity was unable to do so and the Maperton Trust has been told to remove from its website all claims that the badge can repel head lice.
Other items for sale on the charity's website include an "Automatic Universal Remedy Maker", priced at £3,600, that the charity says can "copy and make energetic remedies" and can "broadcast treatment to a person, animal, plant or soil at a distance".
A spokeswoman for the Maperton Trust declined to comment.