Background/Objectives: Lack of objective evidence exists regarding changes in physical function and impact on daily functioning in paediatric post-COVID-19 condition (PPCC). This study aimed to assess exercise capacity, fatigue, and peripheral and respiratory muscle strength in PPCC patients compared with healthy controls. Additionally, the impact of PPCC on domains of daily life was evaluated. Methods: A cross-sectional study was performed. Study variables: exercise capacity (6 min walk test, 6MWT), inspiratory muscle strength (maximal inspiratory pressure, PImax), handgrip strength (handheld dynamometer, HHD), quadriceps femoris muscle thickness (QF MT), rectus femoris muscle thickness (RF MT), rectus femoris cross-sectional area (RF CSA), rectus femoris echo-intensity (RF EI), fatigue (Paediatric Functional Assessment of Chronic Illness Therapy-Fatigue, pedsFACIT-F), and physical activity (Assessment of Physical Activity Levels Questionnaire, APALQ). Results: A total of 115 PPCC patients and 227 healthy controls were included. The PPCC group had lower 6MWT (509.00 ± 86.12, p < 0.001), PImax (68.71 ± 26.23, p < 0.001), HHD (82.84 ± 29.09, p < 0.001), APALQ (7.94 ± 3.14, p < 0.001), pedsFACIT-F (24.51 ± 11.01, p < 0.001), QF MT mid-thigh (33.21 ± 7.99, p = 0.011), and higher RF EI (p < 0.001) vs. controls. Only 37.63% of the PPCC group resumed previous sports, 43.48% were unable to attend school full-time and 28.7% could not participate in after-school activities. Conclusions: Paediatric post-COVID-19 condition patients exhibited significant impairments in terms of physical function, with a high impact on daily functioning. This knowledge is necessary to provide targeted therapeutic interventions.

Background/Objectives: Evidence on pulmonary rehabilitation (PR) in paediatric post-COVID-19 condition (PPCC) is scarce. This study aimed to evaluate the association of a PR programme with changes in physical and mental health and quality of life in PPCC over a 12-month follow-up. Methods: A quasi-experimental pre–post single-arm study was conducted, with no control group, in PPCC patients attending an outpatient PR unit. The primary outcome was change in exercise capacity (6 min walk test, 6MWT). Secondary outcomes included inspiratory and peripheral muscle strength, quadriceps muscle morphology by ultrasound, fatigue, physical activity, quality of life, and psychiatric symptoms, assessed using validated paediatric instruments. Results: A total of 115 PPCC patients (mean age 13.3 years; 66.1% female) completed the PR. 6MWD distance increased from 509 ± 87 to 546 ± 86 (+37 m; p < 0.001; D: 0.50). Handgrip strength increased by 2.4 kg, maximal inspiratory pressure increased by 15 cmH₂O, physical activity increased by 2.4 points, fatigue score improved by 9.3 points, and quality of life improved by 11 points (all p < 0.001). Rectus femoris thickness increased by 0.56 mm (p = 0.005), psychiatric symptom scores decreased by 4.5 points (p < 0.001), and rectus femoris echo-intensity decreased (p = 0.003). Conclusions: Multidisciplinary PR appears feasible and potentially effective in improving physical function, psychological well-being, and quality of life in PPCC, supporting the need for evidence-based paediatric rehabilitation.