The overall goal of this study is to develop and improve assessment methods for children with and without perinatal arterial ischemic stroke (PAS)/hemiparetic cerebral palsy (HCP). The focus is on behaviors of the arms and hands and includes other domains of child development like fine motor, gross motor, language, cognition, and social-emotional skills. This study involves 1) the use of data, including video recordings, from I-ACQUIRE - Perinatal Arterial Stroke: A Multi-site RCT of Intensive Infant Rehabilitation (NCT03910075) and 2) a prospective longitudinal observational data collection with a typically developing cohort using a comprehensive assessment battery (play, fine motor, gross motor, language, cognition, and social emotional skills). The current study is called the BAM Index. No intervention or treatment is provided as part of the BAM Index. The I-ACQUIRE study is an RCT that includes an intervention. The BAM index study is a use of data from the I-ACQUIRE cohorts and a prospective observational study of a typically developing cohort (children without stroke or cerebral palsy) over time. The results of this work will develop, test, refine, and validate a new methodology based on reach-and-grasp and other behaviors related to child development that will have profound and lasting impact on assessment and selection of treatment strategies for pediatric physical rehabilitation of children. The use and reuse of video technology is also well-suited to remote or virtual assessment. This proposal will add to our current knowledge by 1) yielding a psychometrically robust and alternative approach to measuring upper extremity function in children with stroke and/or hemiparetic cerebral palsy and 2) defining specific parameters about how to promote closer-to-normal upper extremity function in children with motor disability.