The two-year-old girl was spotted alone beside a busy road in a coastal resort while her parents drank 100 yards away.
Police arrived to find the child in tears, being comforted by local people. The parents showed no concern for their daughter and became abusive when questioned, police said yesterday.
Officers fed her soup and water in a cafe in Carcavelos, 10 miles west of the capital Lisbon, before taking her to a police station where she reportedly wolfed down a meal of fish and cooked vegetables.
State prosecutors were considering whether to bring charges.
"The girl was playing on her own right next to a dangerous busy road," a police spokesman said.
"Passers-by were obviously concerned for her safety because she was in a risky situation, so they took her and put her in a buggy.
"They called the police, and when we arrived she was crying in her buggy and was obviously hungry and thirsty."
Officers gave the child food and drink while they tracked down her parents.
"They were clearly very drunk and officers tried to speak to them in several languages but they refused to acknowledge the officers," the spokesman added.
"Later they became very abusive."
The girl was then taken to the police station and given dry clothes, as she was wet, and more food. "She ate very quickly," he said.
The parents were also taken to the police station but were too drunk to speak properly. They were not arrested but a file has been sent to the state prosecutors.
"They showed absolutely no concern for her welfare so she was taken into care," the spokesman said.
The girl spent the night at an emergency centre for children and was believed still to be there yesterday, having been found on Monday. A court will decide whether she is returned to her parents.
Her parents are middle-class teachers aged 40 and 38 on holiday from Britain, according to the Portuguese daily Diario de Noticias, although another newspaper said that they lived in Carcavelos and worked as teachers in Lisbon.
The police spokesman said that they gave an address in Portugal but could not confirm whether it was their home address.
Rui Vasconcelos, one of the officers who rescued the girl, said: "Witnesses said the couple were sitting on the promenade from 4.30pm. It was 7.30pm when we arrived and we found the man drunk. The woman could not even get up from the table."