Veronica Panarello wept as the sentence was read out, Rai News reported.
She is accused of strangling her child, Loris Stival, in November 2014, before throwing his body into a pit near the family home.
A Ragusa judge, Andrea Reale, said that the murder had been premeditated and was carried out with "cruelty"; Panarello allegedly hid the body while the boy was still alive, but unconscious.
The child's body was found in a canal by a hunter in the small town of Santa Croce Camerina, south-east Sicily. He had suffered a severe head wound and had scratch marks on his body.
Investigations into Panarello began shortly after the discovery, but she has protested her innocence throughout the trial.
Initially, she had told police that her son had not come home from school on the afternoon in question, before later saying his death was an "accident", which occurred while he was playing with electric cables.
She then blamed the child's paternal grandfather, Andrea Stival, saying she had been having an affair with him and that Stival had killed the boy to stop him telling anyone about it. Panarello claimed Stival had strangled Loris after asking her to tie the boy's wrists.
Panarello's lawyer, Francesco Villardita, announced her intention to appeal Monday's verdict.
She now also faces charges of slander against her father-in-law.
Prosecutor Marco Rota said: "There is no 'satisfaction' with the sentence, but the knowledge of having done our duty," according to Rai.