Brother and sister Olly and Charlotte McIlroy, from Bexleyheath, spent more than £2,000 on four handsets for their family.
The pair were drawn to the 5S Touch ID technology which allows users to unlock their phone with the touch of a finger.
The queue snaked around a packed Regent's Park, with several people carrying tents and energy drinks as they made their way towards the store from 8am.
More top news
Police have warned the drug, known locally as "pink champagne", could be deadly.
The author said "It's been wonderful" as fans mark two decades since the children's books opened up a world of magic to millions.
There was something very striking about the pact, which implies the new agreement could remain in place even if the prime minister does not.