The pair, ages 14 and 15, are also suspected of another robbery on Tuesday, the day after Paula Castle was mugged in an alley in Greenford, a suburban neighborhood in western London, The Daily Telegraph reported.
Witnesses said two men came up behind Castle, 85, and seized her purse, knocking her down. The handbag was found nearby.
The teenagers were arrested Wednesday, a spokesman for the Metropolitan Police said.
The place where Castle fell had a single bunch of flowers tied to a railing Wednesday with a card: "RIP (lady in alley). What a senseless waste of a good life xxx."