Local reports say the driver was three times over the drink-drive limit.
An Irish boy, believed to be around 5-years of age, has been injured in a hit-and-run in Spain.
The incident happened in the coastal resort of Salou on Monday night.
Reports say the driver later turned himself in at around midnight, after he failed a breath test.
The vehicle that struck the boy was a Mediterranean Games official car.
The suspect driver was arrested after going into a local police station around 45 minutes after the 11.45pm accident. Local reports said he was three times over the drink-drive limit.
A spokesman for the Mediterranean Games Tarragona 2018 said in a statement: "We can confirm a traffic accident in Salou involved an official vehicle driven by a man working for a sub-contracted firm who was not a direct employee of the organising committee.
"As a result of the accident a five-year-old Irish boy was injured and was taken to the Joan XXIII Hospital in Tarragona.
"The youngster is in intensive care but he is progressing favourably."
The Department of Foreign Affairs says it is offering consular assistance to the family.
