BackgroundLittle research has been done on the signs of child sexual abuse (CSA) in infants and very young children, or on the consequences that such abuse - including the persistence of the abusive pornographic images on the internet - might have for the children and their parents. The effects of CSA can be severe, and a variety of risk- and protective factors, may influence those effects. CSA may affect the psychosocial-, emotional-, cognitive-, and physical development of children, their relationships with their parent(s), and the relations between parents. In the so called `the Amsterdam sexual abuse case’ (ASAC), infants and very young children were victimized by a day-care employee and most of the victims were boys. Research involving the children and their parents would enable recognition of the signs of CSA in very young children and understanding the consequences the abuse might have on the long term.Methods/designThe proposed research project consists of three components:(I) An initial assessment to identify physical- or psychological signs of CSA in infants and very young children who are thought to have been sexually abused (n = 130);(II) A cross-sequential longitudinal study of children who have experienced sexual abuse, or for whom there are strong suspicions;(III) A qualitative study in which interviews are conducted with parents (n = 25) and with therapists treating children from the ASAC. Parents will be interviewed on the perceived condition of their child and family situation, their experiences with the service responses to the abuse, the effects of legal proceedings and media attention, and the impact of knowing that pornographic material has been disseminated on the internet. Therapists will be interviewed on their clinical experiences in treating children and parents.The assessments will extend over a period of several years. The outcome measures will be symptoms of posttraumatic stress disorder (PTSD), dissociative symptoms, age-inappropriate sexual behaviors and knowledge, behavioral problems, attachment disturbances, the quality of parent-child interaction, parental PTSD, parental partner relation, and biological outcomes (BMI and DNA).DiscussionThe ASAC-project would facilitate early detection of symptoms and prompt therapeutic intervention when CSA is suspected in very young children.Electronic supplementary materialThe online version of this article (doi:10.1186/s12888-014-0295-7) contains supplementary material, which is available to authorized users.