-Study participant is 2 to 25 years of age inclusive, at the time of signing the informed consent. No study participants from 2 to <4 years of age will be included in Stage 1 -Study participant is diagnosed with either childhood absence epilepsy (CAE) or juvenile absence epilepsy (JAE) as defined by the International League Against Epilepsy (ILAE) criteria -Study participants 2 to <4 years of age and participants who had onset of absence seizures at an age younger than 4 years must have a negative glucose transporter type 1 deficiency syndrome (GLUT1DS) genetic test -Study participant is untreated with antiepileptic drugs (AEDs) or pretreated for absence seizures with a maximum of 2 historical AEDs, but without AED treatment for a period of at least 5 half-lives of the AED before randomization into this study. The UCB study physician should be consulted if in doubt -Study participant has electroencephalogram (EEG) evidence of bilateral synchronous, symmetric generalized paroxysmal spike waves (2.5-6 hertz) with normal background activity and with at least 1 electrographically recorded seizure lasting 3 seconds or more on a 1-hour EEG with hyperventilation (HV) while awake at Visit 1 (V1), or on a historical EEG up to 12 weeks before enrollment -Study participant has a history of clinically evident absence seizures occurring on at least 3 days per week in the 2 weeks prior to enrollment -Study participant is without treatment with psychoactive drugs or on a stable dose for at least 2 weeks prior to randomization -Study participant has normal neurological examination, head size, development and cognition -Body weight is ≥9 kg -Male and female a) A sexually active male study participant must agree to use contraception during the treatment period and for at least 2 days, corresponding to the time needed to eliminate study treatment, after the last dose of study treatment and refrain from donating sperm during this period b) A female study participant is eligible to participate if she is not pregnant, not breastfeeding, and at least 1 of the following conditions applies: The study participant is premenarchial OR A woman of childbearing potential (WOCBP) who agrees to follow the contraceptive guidance during the treatment period and for at least 2 days after the last dose of study treatment, corresponding to the time needed to eliminate study treatment - Study participant is capable of and provides consent/assent, and the study participant’s parent/legal representative/caregiver provides signed informed consent for minor study participants, which includes compliance with the requirements and restrictions listed in the informed consent form (ICF) and in this protocol