The Scots asked for help from the French.
On 16 June 1548 thousands of French troops arrived at Leith, the port in Edinburgh, and attacked the town of Haddington with artillery.
During this siege on 7 July, the Scots and French signed the Treaty of Haddington. This promised that Mary would marry Dauphin Francis - the heir to the French throne.
The Earl of Arran had persuaded the Scottish Parliament to favour a French marriage for the Queen.
The French fleet sailed to Dumbarton and left for France with the young Mary and her four young attendants - known as 'the four Marys'.
In France, Mary was brought up in the Catholic faith. In April 1558 Mary married the Dauphin Francis. A year later the King of France died. Francis and Mary now became King and Queen of France.
Mary also became used to French customs and language before returning to Scotland in 1561. Meanwhile, in Scotland, Mary’s mother became Regent.