Acute lymphoblastic leukemia is the most common type of cancer in children diagnosed between the ages of two and five. After cancer treatment, children suffer from fatigue and exhaustion, and thus a decrease in daily physical activity. In addition, lack of physical activity and sports causes a decrease in strength and mobility and affects coordination of movements, proprioceptive perception and balance, which can lead to the occurrence of many injuries. In addition, physical inactivity in children who have survived cancer increases the risk of cardiovascular diseases or causes overweight and obesity. In addition, the separation of children with cancer from their peers harms social, emotional, physical and school indicators of quality of life. The aim of the project is to determine the impact of 12 weeks of buddy-movement therapy on the psychomotor and social development of pediatric cancer patients in remission. The investigators expect a significant improvement in the motor skills of pediatric oncology patients in remission, specifically in fine and gross motor skills, in coordination of both hands, in body coordination, in strength and dexterity. The investigators also assume that after the introduction of 12-week buddy-movement therapy, there will be a significant improvement in the quality of life of pediatric oncology patients in remission, specifically in emotional functioning, in social functioning, in physical functioning and in school functioning. Furthermore, it is anticipated that after the introduction of 12-week buddy-movement therapy, the study will notice significant differences in motor skills between the experimental and control groups. It is also assumed that after the introduction of 12-week buddy-movement therapy, significant differences in quality of life between the experimental and control groups will be observed. The research will involve pediatric oncology patients in remission aged 5 to 12 years with acute lymphoblastic leukemia - ALL, who are treated at the Department of Pediatric Hematology and Oncology of the National Institute of Children's Diseases (NÚDCH). The research participants will undergo an entry and exit examination, including body mass index (BMI; kg/m^2) calculated from weight (kg), height (m), waist circumference (cm), hip circumference (cm), psychomotor examination using the Bruininks-Oseretsky Test of Motor Proficiency, Second Edition, and quality of life measured by the Pediatric Quality of Life Inventory. They will be divided into a control and experimental group, with the experimental group undergoing a 12-week Buddy-movement therapy focused on the development of psychomotor skills and socialization of participants using Buddy peer support.

Acute lymphoblastic leukemia (hereinafter referred to as ALL) is the most common cancer in children diagnosed between the second and fifth year of life. It is a highly aggressive type of leukemia that arises from the malignant proliferation of cells in a child's gland or bone marrow. Currently, thanks to multimodality treatment, including surgical treatment, radiotherapy, and chemotherapy, more than 75% of pediatric oncology patients can be cured. The treatment of ALL is very difficult and possible only in hemato-oncology centers, which causes the separation of children with cancer from the group of peers and has a negative impact, above all, on social, emotional, physical, and school quality of life indicators. The demanding course of treatment makes it impossible for children to participate in joint sports and play activities, which play an important role in the psychosocial development of children and adolescents. During chemotherapy in children and ALL, there is fatigue and a significant decrease in activity level, manifested by motor delays and limitations in activity, including problems with flexibility, posture, walking balance, or functional mobility. Other undesirable side effects include a decrease in physical fitness, a low level of cardiorespiratory fitness, a deficit in muscle strength, or a decrease in bone mineral density, etc. In addition to general weakness and pain, impairment of physical performance is also attributed to muscle atrophy, which may be the result of malnutrition, inflammation, lack of exercise, or side effects of glucocorticoid treatment. In addition, physical inactivity in child cancer survivors increases the risk of cardiovascular disease or is the cause of increasing overweight and obesity. Given the key role that physical activity plays in this developmental period, the problem of physical inactivity is becoming increasingly worrisome. Studies show that more than 50% of cancer patients in remission do not meet the CDC recommendations for 60 minutes of moderate to vigorous physical activity. Children who have survived cancer are generally less physically active than healthy children, which is usually associated precisely with psychological indicators of quality of life, with a decrease in self-esteem, fear of ridicule, as well as with feelings of inability and incompetence to integrate into existing social relationships between peers. Although considerable progress has been achieved in the field of pediatric oncology and medical treatment of ALL, effective therapeutic procedures reflecting the psychomotor and social delays of cured pediatric oncology patients are currently still absent.

Inclusion Criteria:

• Age: 5-12 years
• Diagnosis: acute lymphoblastic leukemia in complete remission
• First-line treatment of acute lymphoblastic leukemia according to the treatment protocol
• BUDDY - a healthy friend aged 5-12 years

Exclusion Criteria:

• Participation in the movement program less than 80%