Patients' gait quality is assessed using a minimal version of the Quantified Gait Analysis (QGA), which simply includes spatiotemporal, kinematic and electromyographic gait parameters. To this end, 10-meter barefoot walking tests at spontaneous (2 trials), fast (2 trials) and double-task speeds, i.e. walking and listing animal names (1 trial) and fruit names (1 trial), and finally with usual shoes and orthoses, are carried out. Walking tests are performed in comfortable clothing, as close to the body as possible, with uncovered legs (shorts). A walking frame is authorized for children who cannot walk 10 meters without one. The total duration of the assessment for the child is 20 minutes.

Walking endurance is assessed by the 6-minute walking test (TDM6). According to the instructions for this test, the distance covered in 6 minutes is observed. Children are asked to walk as far as possible in 6 minutes on a 60-meter marked track in corridors. Children are fitted with shoes, orthoses and/or walking aids, depending on their habits. Footwear and technical aids must be identical between the 3 evaluation times T0, T1 and T2. An indication of the remaining test time is given to the children every minute by the investigator. The duration of the test for the child is estimated at 10 minutes.

Somatosensory function is measured by the cortico-cinematic coherence (CKC) index, which reflects the correlation between electrical activity in the primary sensorimotor cortex (measured by conventional low-density electroencephalogram (EEG)) and displacement of the center of pressure (CoP) in standing static equilibrium for 2 minutes (measured by a force platform). This exploratory index will enable us to estimate the cortical processing of proprioceptive afferents in the lower limbs. The estimated duration of this measurement is 10 minutes.

Balance is assessed by 30-second unipodal hold tests (1 trial), if possible for the child, and 30-second bipodal hold tests under open-eye (1 trial), closed-eye (1 trial), foam (1 trial) and double-task conditions, i.e. counting backwards from 50 (1 trial). These tests are performed on a force platform (AMTI Accusway) to record the CoP's trajectory. The evaluation is scheduled to last 10 minutes.

The GMFM-66 is a 66-item quantitative observational scale for assessing gross motor function in children with cerebral palsy (CP). Five dimensions of gross motor function are tested: Dimension A: lying and rolling, Dimension B: sitting, Dimension C: crawling and kneeling, Dimension D: standing, Dimension E: walking, running and jumping. Each item is scored on a 4-point scale, depending on whether the task requested by the investigator has been completed in full or in part. A maximum of three trials is allowed, and any spontaneous performance is accepted. The GMFM 66 takes around 45 minutes to complete.

For children with neuromuscular disorders (NMD), the Motor Function Measure (MFM). The MFM is a quantitative observational scale comprising 32 items, divided into 3 domains: domain D1: standing and transfer, domain D2: axial and proximal function, and domain D3: distal function. Each item assesses a specific motor task, and performance is rated on a scale from 0 to 3. The child is asked to perform the various MFM tasks. The MFM takes around 45 minutes to complete.

Quality of life is assessed by the KIDSCREEN questionnaire. The KIDSCREEN-27 measures health-related quality of life in children and adolescents aged 8 to 18, across five dimensions: physical well-being, psychological well-being, autonomy and relationships with parents, social support and relationships with peers, and school environment. In this study, only the dimensions of physical well-being, psychological well-being, autonomy and relationships with parents are assessed. The questionnaire is completed by the child, unless under 8 years of age. Approximate completion time for children is 5 minutes.

Achievement of daily activities and mobility is assessed by the Pediatric Evaluation of Disability Inventory as a Computer Adaptive Test (PEDI-CAT). The PEDI-CAT measures the functional abilities of children with disabilities in four functional domains: activities of daily living, mobility, social and cognitive activities, and responsibility. The daily activities and mobility domains are assessed. The questionnaire is completed online during the consultation by the child accompanied by at least one parent. It takes approximately 15 minutes for the child to complete the questionnaire online.

Daily physical activity (PA) is measured using an actimeter (Actigraph GT3X). The following parameters are observed: number of daily steps, time spent at different levels of phsyical activity intensity (sedentary, light, moderate to vigorous), and time spent in different positions (lying, sitting, standing). The actimeter is worn on a belt during the day and on the wrist at night, for 7 consecutive days before or after each visit.

The short version of the User Experience Questionnaire (UEQ-S) is used. It contains 8 items grouped into two scales: pragmatic qualities (efficiency, insight, reliability) and hedonic qualities (stimulation, novelty). The format of the items is a semantic differential (e.g. Complicated - Simple) with a 7-point Likert scale. This questionnaire was chosen because it is the most widely used in the literature and has already been used with children.

The Usability Metric for User Experience (UMUX) is a short 4-item questionnaire. The items are statements about ease of use and usefulness, with which respondents express agreement on a 7-point Likert scale. The UMUX is strongly correlated with the System Usability Scale (SUS), which is the most widely used usability questionnaire, with a large amount of associated research literature, but contains 10 items. The scores obtained on the UMUX are therefore used to position the solution's usability on the SUS interpretation scale ("worst imaginable", "poor", "acceptable", "good", 'excellent' or "best imaginable").

The MARS (Mobile Applications Rating Scale user version) comprises 23 items divided into 6 domains. We will examine the first 3 domains: engagement, functionality and aesthetics. Answers are given on 5-point Likert scales.