Medical events such as severe injuries and life-threatening illnesses are diagnosed as potentially traumatic events. Among fatal diseases, childhood cancer is frequently considered as a traumatic event (
1). When children are exposed to the situation in which their siblings are suffering from life-threatening illnesses, such as cancer, they are usually unprepared and find themselves in a critical situation. Such events affect the pattern of family life so that they experience disintegration of life every day and confront the unpleasant feeling of tension (
2). Bowlby’s theory of attachment suggests that if a child in this situation perceives the threat to the life of their sibling who is deeply connected to, it results in anxiety and grief (
3). Grief, as an emotion, is differently experienced by each individual and is partly dependent on the individual’s stage of life (
2,
3). Reaction to death depends on the child’s maturity, personal experiences, and their understanding of death consequences (
2,
4-
6). Reactions to grief over the death of a sibling typically include severe sadness and depression for prolonged periods. Aggression is a common reaction and siblings may have behavioral problems (
2,
7). Eilegard et al. in a survey on 174 bereaved siblings and 219 non- bereaved siblings’ experience showed that bereaved siblings had low self-esteem, minimum personal growth, and high levels of anxiety and depression (
8). Reactions to death in children may be multifaceted and include cognitive distortions, strong emotions, physical issues, and psychological adjustment disorders (
9). Grief for siblings is inadvertently ignored because the emphasis of social and family support is constantly on the parent’s loss experience (
10). Also, the grief of these children may be not visible to other family members in the crisis because they are focusing on the death of the deceased child at this time (
11-
13). In addition, most children are well aware that their parents are disturbed and saddened by the death of their deceased child, so they do not express their own inner problems in order not to add to their parents’ grief. Furthermore, these children usually do not express their feelings freely, and this may mislead family members to think that the child is doing well. For this reason, and also because of the preoccupations, pain, and anguish of parents they often neglect the needs of bereaved siblings (
13). Maercker reported that this could lead to the development of persistent complex bereavement disorder in surviving siblings, also known as prolonged grief disorder (PGD) (
14). PGD is a proposed diagnostic category that is intended to classify bereaved individuals who experience notable dysfunction for atypically long periods of time following a significant loss (
15). Core symptoms include a pervasive yearning for the deceased or persistent preoccupation with the deceased accompanied by intense emotional pain (
16), a syndrome, which occurs in about 10% of bereaved adults. Similar to adults, 10% of children who are bereaved by sudden parental death have high and sustained prolonged grief reactions (PGR) nearly 3 years after death (
17). A case study by Allen et al. (
18) on a 16-year-old boy showed that he was experiencing symptoms of depression, anxiety, physical symptoms, and Post-traumatic stress disorder (PTSD) 8 years after the death of his older brother in an accident. In individual treatment sessions, he reported feeling guilt for his older brother’s death and anger with his mother for not speaking openly with him about his brother’s death (
18). Many previous studies have shown that childhood cancer-related PTSD by focusing on the parents or the patient, and siblings have typically been excluded from these studies while they have witnessed pain, the severity of illness, or loss of weight and hair of their sick siblings. In addition, they may be away from the child with cancer for a long time, being afraid of their death possibility, do not understand the disease and treatment process, and greatly lose their parents’ support because of being involved in the patient’s treatment process. Furthermore, their daily routines being disrupted, and they have to stay with relatives or friends (
1,
11,
19,
20). The results of a recent systematic review of the psychological adjustment of siblings of children with cancer showed that they are at risk for adjustment disorders and suggested that the distresses they experience can be conceptualized in a PTSD framework. They reported that 29% - 38% of siblings of children with cancer experience moderate to severe PTSD symptoms (
1,
21). In a study in 2013, Kaplan et al. (
1) showed that more than 60% of siblings of children with cancer reported moderate to severe PTSD, and 22% of them had all of the PTSD criteria. Considering the adjustment problems of siblings of children with cancer during illness, conditions that the family experiences before the death of the child, and major changes that occur after the death, these children often appear to face with problems that require early and appropriate psychological interventions to prevent more serious harm in subsequent years of development. However, much of the research on child bereavement has focused on losing a parent and limited research has been done on children who have experienced sibling loss (
22-
24). Numerous approaches have been proposed based on different approaches to the treatment of PGD. While these interventions usually emphasize the importance of talking about the lost person and feelings of grief, children are unable to express their emotions and feelings due to their low level of abstract thinking (
25). Some of them avoid talking about their loss in order not to face the reality, pain and consequences of their loved one’s death (
26). Theraplay is based on the Bowlby’s theory of attachment, where treatment is adjusted according to the early stages of the child’s development, where the child’s emotional development stops, and the attachment process is disrupted. Theraplay can explore the emotions and feelings of these children and provide them with a positive, warm and compassionate care, and a sense of value, as well as, fulfil their needs to adjust to their emotions and the child can achieve what they have lost before. Theraplay is not based on cognitive representation but rather on emotions and can be applicable to a wide range of emotional, social, and behavioral problems at different ages from childhood to adulthood (
3,
27). In general, the main focus of this intervention is on connection, and its therapeutic model is based on the attachment theory including sensitive, responsive, and playful interaction between the caregiver and the child to facilitate child development, create positive internal working models of self and others, and its long-term impact on the child’s behavior and emotions. Activities are not the key to Theraplay efficiency! Rather, activities are merely tools that facilitate connection. The key is to pay attention to the child and to teach parents to pay attention to the child and to “wholeheartedly” help children become healthier and happier. This method is useful for all ages, from infancy to adolescence, but is used in the age range of 18 months to 12 years (
28).The results of a study by Makela and Vierikko (
29) have shown that Theraplay is effective for both boys and girls in reducing behavioral and emotional problems, especially aggressive behaviors, and this reduction has been persistent in follow-up studies. The goal of this treatment was to help the child to adjust their emotions and behaviors and challenge their negative internal working models (
30).