Two siblings have died after drinking caustic soda, with a three-year-old boy mistaking the acid for a fizzy drink and his 13-year-old sister ingesting it after feeling guilty for leaving it out on the table.

The incident took place in the city of Santo Amaro, which is located in the north-eastern Brazilian state of Bahia on Monday 6th December.

The two siblings died after drinking the sodium hydroxide, which is also known as caustic soda, according to the police.

The three-year-old boy, who has not been named, is believed to have mistaken the deadly acid for a fizzy drink and picked it up of a table before drinking it.

His older sister, also unnamed but aged 13, is said to have felt guilty and ingested the substance as well.

The two siblings were taken to hospital for treatment but they sadly died.

The two were said to have been alone at home at the time of the incident and according to Santo Amaro delegate Rafael Almeida de Oliveira, the children’s mother, who has not been named, had purchased the substance from a shop in order to clean the toilet.

He said: “She asked the girl to put it under the sink, but the girl put it on the table. So the boy had access to the product and started drinking it.”

He added: “The 13-year-old girl felt guilty and also drank the substance. I think she could not stand her brother’s suffering. She was also taken to hospital and did not survive.”

The delegate also said that the children’s mother will be indicted and an investigation is currently underway to determine whether or not there was negligence on her behalf.

The delegate added that a judge will have to decide whether or not the mother should be punished, considering she has already suffered with the death of her two children.

He said: “In cases like this, in which the damage affects the suspect, such as the loss of two children, the penalty for the crime is not applied, because it is understood that the mother has already been penalised with the death of her children. But it is up to the judge to decide this.”