A witness described seeing the woman hit the boy in the face with an open hand during a visit to the Gekås store in Ullared in September last year.
The customer told police that the child was “absolutely distraught and screamed and cried”.
The mother said the boy had been misbehaving at the time, Hallands Nyheter reports. She admitted striking the child lightly, but said she had acted instinctively after he spat at her.
Varberg District Court has now found the woman guilty of minor assault and fined her 2,500 kronor ($285). The court has also ordered her to pay 5,000 kronor in damages to her child.
Sweden was the first country to introduce a formal ban on corporal punishment of children in 1979. Children enjoy the same legal protection from physical assault afforded to adults.