If this is just a day camp you will have to keep things fairly simply and focus on basic skill instruction. What I did while coaching in Europe in a club was to create a series of camps about every 2-3 months which progressively covered more topics and skills. If the kids are staying overnight during these 12 days than you have more flexibility. If this is the case I would organize your days into 3 sessions. Morning, afternoon and evening.
Mornings are best for teaching because the kids are fresh and alert.
Afternoons are good for repetition of skills, and some games, and evenings are best reserved for games and fun. I think giving kids some release from the pressure of long workout hours is critical at this age because they are so un-prepared to practice extended hours. There are enough problems running camps that arise even when you are totally prepared. In terms of session length. While kids this age are physically very pliable the habits you teach them regarding the importance of stretching, taking care of injuries, warming-up properly are habits they will take through their basketball lives.