Introduction This study assesses the cognitive functions of children with brain tumor, including orientation, spatial perception, praxis, visuomotor constructions and thinking operations. The aim of the study was to assess the cognitive functions of children with brain tumor in the treatment process and the effects of different treatments on cognitive functionality. Method Cognitive functions of children with brain tumor (n = 102) and children with typical development (n = 90) were assessed with the Dynamic Occupational Therapy Assessment for Children. Children with brain tumor were divided into four subgroups according to the treatment they received. Multiple comparisons were analyzed using the Kruskal-Wallis test and binary comparisons were analyzed using the Mann-WhitneyUtest. Results Cognitive functions of children with brain tumor were weaker than children with typical development. Children who received chemotherapy, radiotherapy, surgery and both chemotherapy and radiotherapy had weaker cognitive functions. Conclusions Children with brain tumor whose treatment process is continuing are cognitively affected and their occupational performance in daily living tasks is weakened. In these children, cognitive- and occupation-based early intervention approaches should be developed and implemented. Especially when children start receiving radiotherapy, it may also be useful to start cognitive occupational therapy programs simultaneously for preserving children's cognitive functionality.