The children's referendum will go ahead despite the Government being found to have wrongly used a 1.1 million euro fund in some of its publicity campaign.
The Supreme Court ruled that extensive passages in an information booklet and on a website were in breach of rules designed to ensure a fair, equal and impartial playing field in a referendum debate.
Children's Minister Frances Fitzgerald said: "In providing public information the Government at all times acted in good faith and with the best of intentions in informing people about the substance of the amendment.
"The approach taken was supported by legal advice and reflected the understanding at the time of the legal requirements in this complex area of law. However, I fully acknowledge the Supreme Court has found that not all of the material published complied with the McKenna principles."
The case was taken by Dublin-based engineer Mark McCrystal who contested that the Government was in breach of rules set down by the 1995 McKenna judgment which bars public funds being used to promote a vote one way or another in a referendum.
Justice Minister Alan Shatter insisted Saturday's poll will not be delayed by the judgment. After the ruling, the Government's website childrensreferendum.ie was taken off line.
After examining the information campaign, the Supreme Court found that some of the material included a misstatement, which the Government had admitted to, in relation to the effect of the referendum.
"The Constitution belongs to the people and may be amended only by the people in a referendum. It is this democratic process which is protected by the McKenna principles," the court said. "Public funding should not be used in a referendum to espouse a particular point of view."
The ruling also said that not all publications and information issued through the Referendum Commission were in breach. Mr McCrystal said he had written to the Government in advance of the court challenge and accused officials of dismissing his concerns. The High Court had rejected his claim.
"I think politicians should hang their head in shame over this," he said.