Aim: Diastasis recti is a common contour abnormality of the anterior abdominal wall, where an increased distance between the rectus abdominis muscles results in a visible or palpable bulge in this area. This study aimed to characterize this clinical entity in children. Material and methods: Anatomy of the rectus abdominis muscles and the linea alba, with a special focus on the interrectus distance (distance between two bellies of the rectus abdominis muscles), was studied using ultrasound. Anthropometric and ultrasonographic assessments were performed on 38 children aged 7–12 years. According to the clinical definition of bulging in the epigastrium, diastasis was diagnosed in 12 children (31.6%), significantly more often in boys than in girls (50.0% vs. 6.3%). Other clinical and anthropometric variables, such as age, history of preterm birth, body mass, body mass index, waist circumference, and height, were not significantly associated with diastasis recti. Results: Diastasis recti, defined by the ultrasonographic criterion of interrectus distance >20 mm, was found in 10 children (26.3%), with no significant differences between boys and girls. Still, there was a moderate agreement between these two modes of diagnosing diastasis: the Cohen’s kappa coefficient was 0.49. This suggests that ultrasonographic measurement of the interrectus distance should not be considered an alternative and more precise method of diagnosing diastasis. Conclusions: Our study indicates that diastasis recti is quite common in the pediatric population, especially among boys. However, more studies are needed in children to understand the functional relevance and natural course of this clinical entity.