L'échange des princesses

In 1721, the Regent of France, wanting to seal the peace with Spain, offers to the Spanish King, a marriage between their respective heirs: Louis XV, age 11, and Maria Anna Victoria, the 4-year-old Spanish Infanta (princess). The Regent of France also offers to marry his daughter, Mademoiselle deè Montpensier, 12, to the Prince of Asturias, the 14-year-old heir apparent to the Spanish throne. Everything has been done to expect the best of the children, but nothing will proceed as planned., (imdb