Well... I will try to give you an answer, QueenEna.
King Ferdinand VII was married four times. The first wife was his cousin Maria Antonia of the Two-Sicilies, and they had no children. The second wife was his niece Maria Isabel of Braganza (the father was Joao VI of Portugal and the mother Carlota Joaquina of Spain), and they had a daughter (the infanta Maria Luisa Isabel) who lived only four months. The third wife was Maria Josefa of Saxony, and no children were born from this marriage. When Maria Josefa was dead, the king Ferdinad was really desesperate to marry another princess as soon as posible because he needed to father an heir to his crown. So, he married his niece Maria Cristina of Two-Sicilies just seven months after the death of Maria Josefa.
The wedding of Ferdinand and Maria Cristina was celebrated on 11th December 1829. A month later, she became pregnant, and she gave birth to a daughter named Isabel the 10th October 1830. Of course, the royal couple wished a son, but they were glad with the daughter. When Maria Cristina had a second daughter, Luisa Fernanda, the queen persuaded the king to change the succesion laws to permit females to inherit the crown. In fact, Maria Cristina claimed that the old spanish law allowed the woman to inherit the crown, and just when the first king of de Bourbon dinasty (Felipe V) went to Spain it was reemplaced for a salic law. Ferdinand was under a strong influence of his young wife...and he worked very hard to set asside the law of sucession of his ancestry Felipe V. But the brother of Ferdinand, infante Carlos, until this moment heir presumptive of the king, considered the Pragmatic Sanction (the new decree allowing daughters to suceed as well as sons) illegal. Ferdinand knew that his brother had the support of Roman Catholic Church and the more conservative people, so he tried to banish his brother and sister-in-law, princess of Beira: the two were "authorised" by the king to go to Portugal for a time. But it was not a good idea.
Ferdinand was died the 29th September 1833. His widow, Maria Cristina, proclaimed herself regent for Isabel, just three years old, in Madrid, but the first day of October, infante Carlos issued a manifiesto declaring himself the king Carlos V of Spain. It was the beginning of the Carlist Wars.
I don´t believe that Isabel had a happy childhood. The mother and regent Maria Cristina remained as a widow only for... ¡¡three months!!. The 28th December 1833, Maria Cristina married in secret Fernando Muñoz Sánchez, an ex-sargeant from the Royal Guard. For SEVEN years, the couple tried to keep the marriage secret, a very difficult thing, due the fact they had a lot of children: from 1834 until 1840, the year the marriage was announced, the queen regent gave birth to three daughters and two sons, half-sisters and half-brothers of the little queen Isabel. The gossip, first, and the news, later, about the morganatic marriage of the queen to a low-ranking soldier made Maria Cristina really unpopular. This was one of the reasons because the general Espartero replaced her as regent. Maria Cristina and the husband were exiled in France.
Remember that Isabel had nine years when the mother was banished from court and sent to another country with the new family. The new regent and his ministers thought that the little queen was not receiving a good education, so they determined that Isabel and Luisa Fernanda needed a new tutor, Agustín Argüelles (a lawyer), a new teacher (Quintana, a poet) and a new nurse (the countess of Espoz y Mina). The struggles between liberals and conservatives made Espartero forced to exile in England two years later. A military pronunciamiento led by O´Donnell gave a new governement to Narvaez. So, when Isabel was just thirteen years old , she was proclaimed queen by the new cabinet, and when she was just sixteen years old, the same cabinet forced her to marry her cousin, the homosexual Francisco of Asis.
