SARS-CoV-2 infection in adults causes, in about one-third of cases, a persistent impairment in everyday life or exercise tolerance, known as long-COVID. Although several studies are looking at long-COVID in children, there are reports about lung function decline in pediatric COVID-19 survivors are scanty. As part of a post-COVID follow-up program, we enrolled 13 children in performing a cardiopulmonary exercise test (CPET) on an electronically braked cycle ergometer, using an incremental protocol tailored to the sex, age, and weight of the patient. The study cohort was composed of ten males and three females, median age of 12.1 years, all with a previous history of a moderate or severe COVID-19 six months before. A mild form of asthma affected two patients, and one was obese. Notwithstanding five children reported easy fatigue during daily activities, only one interrupted the test due to muscle exhaustion during CPET. The work rate and peak oxygen uptake resulted in the normal range in all patients. Additionally, the breathing reserve and the oxygen pulse were within the normal limit in all subjects, indicating a normal cardiopulmonary function under exercise. These results confirm and extend previous reports of apparent resolution of COVID-19 in pediatric patients and provide preliminary data to support the hypothesis that, differently from adults, COVID-19 in children did not significantly produce permanent damage to lung tissue. Further research is warranted to confirm better and extend these preliminary results and better understand residual symptoms after SARS-CoV-2 infection.