Two young brothers were robbed after they drew out their disabled father's benefit money for him from an Eastbourne post office.
The boys, aged 10 and 12, were approached by a man as they collected £110 from the post office in Etchingham Road.
Police said the man, in his mid-thirties, forced the terrified youngsters to the ground before demanding the cash.
A police spokesman said: "This was a frightening ordeal for the young victims in broad daylight in a bustling community in the centre of Langney."
The thief was of medium build, with several days' stubble and was wearing a white baseball cap, a cream jacket and blue trousers.
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