The woman, from the Stroud area of Gloucestershire, pretended her son was on chemotherapy for three years, starting when her son was four years old.
But now she is facing prison after she admitted child cruelty, fraud and forgery.
Prosecutor Lisa Hennessy said: "The Crown say the defendant claimed that her child had cancer and shaved his head and eyebrows and claimed her other children had various disabilities never diagnosed."
In total, the woman claimed £34,396 in disability living allowances and £18,734 in child cancer benefits despite her son, who is now nine, being in good health.
The woman, who cannot be named to protect the identity of her son, also admitted fraudulently obtaining disability living allowance for her daughter by claiming she was ill.
The mother will be sentenced in November, pending psychiatric reports.
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