A Study to Evaluate the Pharmacokinetics, Safety and Tolerability of Mirabegron Oral Suspension in Pediatric Subjects From 3 to Less Than 12 Years of Age With Neurogenic Detrusor Overactivity (NDO) or Overactive Bladder (OAB)

Inclusion Criteria: * Subject is male or female from 3 to less than 12 years of age. * Subject has a documented diagnosis according to the International Children's Continence Society (ICCS) criteria of: * NDO, or * Idiopathic OAB * Subject's weight/height: * Subject must have a body weight of ≥ 15.0 kg * For NDO: subject is not suffering from malnutrition or is not grossly overweight, in the opinion of the Investigator * For OAB: subject's weight and height are within the normal percentiles (3rd to 97th percentile) according to Centers for Disease Control and Prevention (CDC) growth charts. * Subject is able to swallow the study medication in accordance with the protocol. * Subject and subject's parent(s)/legal guardian agree that the subject will not participate in another interventional study while on treatment. * Subject and subject's parent(s)/legal guardian are willing and able to comply with the study requirements and with the concomitant medication restrictions. * Female subject must: * Be of non-childbearing potential: Clearly pre-menarchal or in the judgment of the Investigator is pre-menarchal. * Or the following inclusion criteria are to be followed, if applicable (rare cases): Female subject that reached puberty must: Agree not to try to become pregnant during the study and for 28 days after the final study drug administration, And have a negative urine pregnancy test predose Day 1, And, if heterosexually active agree to consistently use 2 forms …