April Jones fund was set up as a charity with her parents playing no part in how the money was distributed. At the time the OFM fund was set up there was a police investigation in full swing which could have borne fruit. There was no need for the McCanns to 'search' for Madeleine. There was no reason to set the fund up as a business. The Charity Commission were willing to work with the McCanns to enable the fund to be given charitable status but interestingly the offer was never taken up. All the stranger when you consider that the fund could have added 25p for every £1 donated by U.K. tax payers, a tidy amount.
It was probably set up as a charity as it wasn't formed in order to search for April.
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Because Madeleine's Fund is currently focussed on searching for one child only, Madeleine McCann it cannot register as a charity. However in the future, if the objects of the fund are fulfilled and subsequently changed to concentrate on multiple similar cases, it may then be possible to acquire charitable status.