The “floating ball sign” (FBS) is a rarely described visual phenomenon found in mature ovarian teratoma imaging. It is characterized by the presence of movable, spherical areas within the cystic component of a tumor. Such visualization is possible both in cross-sectional imaging and ultrasonography. To evaluate the incidence of FBS in the pediatric population with regard to patients’ age and tumor size. This is a retrospective study of pediatric patients operated on in a tertiary pediatric surgical center between January 2009 and December 2022 due to mature ovarian teratoma; the medical records were reviewed for the age at diagnosis, recurrences, tumor size, and their characteristics in preoperative imaging. Eighty-three patients (mean age 14, range 0–17) out of 91 met the inclusion criteria for the analysis. Eighty-seven operations on 90 ovaries were performed. Preoperatively 38 patients underwent CT, 13 MRI, and 39 received only the ultrasound examination. The FBS was identified in preoperative imaging diagnostics in 3 (3.3%) girls (14, 16 and 17 years of age). The average largest tumor dimension and volume were 142 mm and 1268 cc in the FBS group, and 73 mm and 252 cc in the remaining group, respectively. FBS tumors usually reach large sizes. Although the sign is rare in children, there are no scientific reports of its occurrence in the first life decade. Color flow mapping and cross-sectional imaging play a pertinent role in distinguishing this uncommon pattern from a malignant mass and enable the selection of an appropriate surgical approach.