Carlota,from what I see,the little prince and princess do not take part in every state dinner.
They were present only at the dinner during the visit of King Juan Carlos.The also welcomed french president FranÁois Hollande and his companion.The royal family seems to have excellent relationships with the spanish royal family and with the different french presidents.For me,it looks more like a family gathering.
Former France first lady Mrs Chirac is a close friend of the family.She was even present at king's niece wedding.
Many french politicians have houses in Morroco.
Even if the king and his sibilings and children were introduced early in public life they don't risk being harrassed by the press
Given that they will remain public figures for the rest of their lives,it's better for them to be accustomed to frequent exposure to the press and public.
Last years,the king doesn't seem to be healthy,therfore it's better to have a well prepared heir.