A Study to Assess Safety and Efficacy of Avalglucosidase Alfa Administered Every Other Week in Pediatric Patients With Infantile-onset Pompe Disease Previously Treated With Alglucosidase Alfa

Inclusion criteria: * The participants has confirmed acid alpha-glucosidase (GAA) enzyme deficiency from any tissue source. * The participants who has reached legal age of majority as defined by local regulation, or the participant's legal guardian(s) must provide signed informed consent prior to performing any study-related procedures. If the participant is legally minor per local regulations, assent shall be obtained from participants, if applicable. * The participants (and participant's legal guardian if participant is legally minor as defined by local regulation) must have the ability to comply with the clinical protocol. * The participants is less than 18 years old. * The participants, if female and of childbearing potential, must have a negative serum pregnancy test (beta-human chorionic gonadotropin) and must not breastfeeding at screening/Baseline. * The participant has cardiomyopathy at the time of diagnosis: i.e., left ventricular mass index (LVMI) equivalent to mean age specific LVMI plus 2 standard deviations. * The participant has been receiving a stable dose of alglucosidase alfa regularly for a minimum of 6 months immediately prior to study entry. * For participants in Stage 1: The participant has documented evidence of clinical decline in at least 1 of the following parameters related to Pompe Disease and not related to intercurrent illness as assessed by the Investigator: respiratory function, motor skills, and/or cardiac parameters. * For participants in St…