TBH, Holy Land Foundation is not some random charity that happened by coincidence to help some orphans whose parents maybe were terrorists. It was a front end for Hamas, them collecting money overseas (measured in millions of dollars) and Hamas controlling and distributing the money on the ground. Hamas has always had, beside its military wing, a large non-military organization, including schools, charities, mosques, libraries, hospitals, sporting clubs, etc. Holy Land Foundation was the part of this framework, and a part of the traditional structure where families of terrorists, either dead or imprisoned, were paid pensions. Each palestinian organization has such program, with PA mostly drawing it from its general budget (US is not too happy about it, as you can imagine, but little can be done to completely prevent it since the money is fungible) and Hamas through its charity network.

So no, it's not just a rumor through an anonymous tipster, it's a well known and established system, which has been operating for years and still is - just not through HLF nowdays, obviously.