A Study to Learn How Effective and Safe the Drug 'Mirabegron' is and How Long it Stays in the Body of Children Aged 6 Months to Less Than 3 Years of Age With Neurogenic Detrusor Overactivity

"Participants will receive mirabegron prolonged-release microgranula-based oral suspension once daily. The initial dose of mirabegron will be based on the participant's weight.~The initial low dose will be up-titrated to a higher dose at weeks 2, 4 or 8 unless the participant is determined to be effectively treated with the low dose, based on urodynamics and the participants'e-diary."