Tracey Jacques was spotted removing items from a £50 toy jet pack box at Smyths Toys, on Portland Retail Park, on March 26, and the knife was recovered at the police station.
In police interview she said she had bought a similar toy for her son which had broken and she had lost the receipt, said prosecutor Robert Carr.
She was last convicted of shoplifting in January 2017, when she received an 18 month conditional discharge at North East Derbyshire and Dales Magistrates Court.
Donna Pursglove, mitigating, said Jacques has learning difficulties and is the sole carer for her son, who was also born with “significant learning difficulties.”
“He is 24 and still likes to play with toys, so I think that gives some indication of his mental abiliities,” she said.
“I think she does understand how seriously the courts view these matters.”
Ms Pursglove said Jacques has a history of theft offences and is taking anti-depressants.
“She has very limited means and when she is under quite severe stress she will commit shop theft offences,” she added. “She stole food to eat on the last occasion.”
Probation officer Raqia Bano said “boredom, stress and a lack of finances contributes to her offending.”
Jacques, 51, of West Street, Doe Lea, Chesterfield, admitted theft and possession of a knife, when she appeared at Mansfield Magistrates Court, on Friday.
Magistrates told her she has “a long history of shoplifting”, and warned her that she would end up in prison.
She was given a 12 month community sentence, with 25 days of a rehabilitation activity requirement.
She was ordered to pay an £85 government surcharge, £85 costs and £50 compensation.