The three-week-old boy died in hospital following the collision on the A75 Gretna to Stranraer road at Hardgrove crossroads, near Carrutherstown, between Dumfries and Annan, during the evening rush hour on Wednesday.
Two other people were taken to Dumfries and Galloway Royal Infirmary and were released after treatment.
Last night campaigners in the Carrutherstown area claimed the Scottish Government bore some responsibility for the tragedy for failing to give the go-ahead to a £10 million improvement project, which would have included the accident scene.
Last year a row broke out when transport minister Keith Brown revealed there was no completion date for the A75 Hardgrove to Kinmount improvement project, ten miles east of Dumfries.
Ann Wright, of Foster Meadow Farm, Carrutherstown, who has been campaigning with others for a road upgrade for the past 20 years, said: “This is not acceptable. This wouldn’t have happened if the government had carried out the work as they promised.
“This road is an important link with the ferries and main routes but unless you are in the north-east of Scotland you don’t get anything from this government.”
Mrs Wright, a farmer’s wife, added: “You can’t really begin to think how these poor parents are feeling after this. It is totally unacceptable and something must be done.”
Dr Elaine Murray, Labour MSP for Dumfriesshire, said: “There is massive support for improvements here. This road must be upgraded as soon as possible to stop any other tragedy like this.”
There have been numerous fatal accidents in the past decade on the Hardthorn stretch of the A75.
The improvement scheme had originally been due to start six years ago to widen three kilometres of the road to give motorists space to overtake safely but the project was delayed because of the economic downturn.
A Transport Scotland spokesman said: “Our sympathies are with family and friends at this time. As police investigations into this accident are ongoing it would be inappropriate to comment further at this time.”
Police appealed for anyone who witnessed the crash, which involved a Honda Civic, a Ford Focus and a Renault Clio, to contact them.
The road was closed for 11 hours and firefighters from Dumfries and Annan were called to the scene to help free those trapped in the wreckage.