Pharmacokinetics, Safety and Efficacy of Nemolizumab in Participants Aged 6 to 23 Months With Moderate-to Severe Atopic Dermatitis

Inclusion Criteria * Participants greater than and equal to (\>=) 6 to less than (\<) 24 months of age at the screening visit. * Diagnosis of AD according to the American Academy of Dermatology Consensus Criteria at the time of the screening visit. * Eczema Area and Severity Index (EASI) score \>= 16 at both screening and baseline visits. * Investigator's Global Assessment (IGA) score \>= 3 (based on the IGA scale ranging from 0 to 4, in which 3 is moderate and 4 is severe) at both screening and baseline visits. * AD involvement \>= 10 percent (%) of body surface area (BSA) at both screening and baseline visits. (Note: BSA to be derived from the SCORing Atopic Dermatitis (SCORAD).) * Weekly average of worst scratch/itch Numeric Rating Scale (WSI-NRS) score of at least 4 at both screening and baseline visits as assessed by the parent(s)/caregiver: * Screening WSI-NRS score will be determined by a single WSI-NRS assessment (score ranging from 0 to 10) for the 24-hour period immediately preceding the screening visit. * Baseline WSI-NRS score will be determined based on the average of daily WSI-NRS scores (score ranging from 0 to 10) during the 7 days immediately preceding baseline (rounding not permitted). A minimum of 4 daily scores out of the 7 days immediately preceding baseline is required for this calculation. For participants who do not have at least 4 daily scores reported during the 7 days immediately preceding the planned enrollment date, enrollment should be post…