Louis César was born at a time when the court was in mourning for Princess Marie-Thérèse of France, known as la petite Madame, who had died in March 1672.

Louis César would grow up with his older brother Louis-Auguste in the care of Madame Scarron in a house on the rue de Vaugirard in Paris.

The next year, while his father was on a military tour at Tournai, he was joined by a sister, Louise Françoise de Bourbon, born in June; Louis César and his parents were present, as well as the Queen Marie Thérèse d'Autriche and Madame Scarron.

On 19 December 1673, Louis XIV officially recognised his children with Montespan with Letters Patent from the Parlement de Paris.

Around the time of Françoise Marie's birth, his mother was supposedly involved in the Affaire des Poisons which made her lose favour with the king.

In 1674, another sister joined the family: Louise Marie Anne was born in November 1674 and was created Mademoiselle de Tours after her legitimisation in 1676.