Inclusion Criteria:  Children aged ≥ 3 years old and < 18 years old. Children with weight ≥ 13 kg Children with chronic neurological disorders (such as polyhandicap, cerebral palsy, Angelman syndrome, Rett's syndrome, epilepsy, amyotrophic lateral sclerosis and mental retardation) Diagnosis of severe sialorrhoea due to a chronic neurological disorder as assessed by a modified Teachers Drooling Scale (mTDS) ≥ 6. DIS Scale ≥ 50. Impact of drooling as assessed by drooling impact scale. Children who have completed at least 3 months of non-pharmacological standard of care treatment (i.e. rehabilitation e.g. intraoral stimulation and oral facial exercise). Children with stable drooling for the past 4 weeks. Written consent form signed by parents (or, when applicable, the subject's legally acceptable representative). Affiliated or beneficiary of a social security scheme. A nominated parent or carer who can commit to complete parent / carer questionnaires, with good ability to understand and speak French. Children testing negative for COVID-19 at start of the trial. (Asymptomatic children with a positive test have the opportunity to have a re-test at least 2 weeks following the initial test and must be negative on the re-test for inclusion).  Exclusion Criteria:  Children unwilling to provide assent to participate in the study. (children who are unable to provide assent should be considered eligible). Botulinum injection for sialorrhoea given within 6 months of enrolment. Any anticholinergic therapy used in the previous 4 weeks. Scopoderm patch used in the previous 4 weeks. History of surgery for drooling in the previous 12 months. Children prescribed non-permitted concomitant medication as defined in section 7.2.2 Children in whom anticholinergics are contraindicated such as those with glaucoma, myasthenia gravis, urinary retention, severe renal impairment, history of intestinal obstruction, ulcerative colitis, paralytic ileus, pyloric stenosis or hypersensitivity to the active substance or the excipient. On-going or programmed orthodontic treatment over the study period. Untreated oro-mandibular dystonia (isolated lingual dystonia accepted), clinical gastro oesophageal reflux, dental inflammatory condition (dental caries, gingivitis…). Family and carers unable to commit to the schedule of the study protocol. Female patients who are lacting or pregnant Female patients who are planning a pregnancy within the study period Patients having participated in another clinical study within at least 30 days or within 5 half-lives of last dose of IMP (whichever is longer). Patients receiving systemic immunosuppressive treatment including cyclosporin, methotrexate, azathioprine cyclophosphamide, mycophenolic acid, anti TNFα, monoclonal antibodies or with congenital immunodeficiency