Agents of Catalonia's police force on Sunday arrested the woman who allegedly drowned her two children aged eight and eleven.
The alleged infanticide took place at a home in the Barcelona neighbourhood of El Carmel, La Gaceta newspaper reported on Sunday.
The mother of the children is said to have been at home alone with her 11-year-old daughter and nine-year-old son at the time of the incident.
Police detained the 35-year-old mother of the children after she was seen wandering the street where she lived in a condition described by neighbours as "agitated".
When the Mossos d'Esquadra, or Catalonia's police, were called, they found two bodies in the main bedroom of the house.
Sources within the police told news agency EFE that autopsies and toxicology reports confirmed the children had been drowned.
Neighbours of the family told reporters the woman had called the father of the children to say she was ready to kill herself.
He then returned to the house to find his dead children.
Social services had apparently been in touch with the family recently because the parents seemed to be on the point of breaking up.
The family was also reported to be suffering financial difficulties.
One neighbour told EFE that the family were about to leave their home because they couldn't afford to pay the rent.
Police are now investigating if the mother had been abused by her husband.
A crowd of about 100 neighbours and interested onlookers gathered in front of the family's building where news of the alleged crime came out.