Interventional Study of Infigratinib in Children < 3 Years Old With Achondroplasia (ACH)

Inclusion Criteria: * Diagnosis of ACH confirmed by genetic testing. If prospective participants had prior genetic testing, the diagnosis must be confirmed by a report from a certified laboratory, documenting the specific mutation. * Age 0 to 32 months (2 years and 8 months) at screening. * Signed informed consent, which must be obtained from each participant's parent(s) or legal guardian. * Parent(s)/Guardian(s) willing and able to attend all study visits and comply with all study requirements. * Parent(s)/Guardian(s) willing and able to comply with the routine care of the study participants according to local guidance for the management of infants and young children with ACH. * Able to swallow age-appropriate oral medication. * In participants \<1 year old, be compliant with recommended vitamin D supplementation of 5 10 μg/day or higher (or as recommended by country specific guidelines). Exclusion Criteria: * Participants who have hypochondroplasia or diagnosis of genetic condition other than ACH, or any clinical condition that can affect growth. * Gestational age at birth \<37 weeks and/or birth weight \<2500 grams. * Gastroesophageal reflux disease requiring prolonged treatment (\>1 week) with prohibited medications. * Evidence of cervicomedullary compression, as defined by an Achondroplasia Foramen Magnum Score (AFMS) 4, symptomatic or asymptomatic, diagnosed during MRI done at screening or a previous MRI done at any time if the participant had not undergone decompres…