Young children aged 0-4 years may be exposed to adverse childhood experiences (ACEs) and/or early life adversity (ELA), which are linked with worse physical and mental health across their lifespan. On the other hand, positive childhood experiences (PCEs) can build resilience and prevent or protect against these detrimental outcomes. Data analyses will assess the interactions of ACEs, PCEs, parenting, and poverty on the early social psychology of childhood and develop objective measures for altered stress regulation using hair cortisol as a chronic stress biomarker.

To elucidate the longitudinal changes underlying HPA-axis dysregulation, using community-based participatory research (CBPR) methods, the investigators have designed a prospective longitudinal study to enroll children aged 6-24 months from families living within Santa Clara, San Mateo, and Alameda Counties. This study will enroll 600 healthy children (as defined by the American Academy of Pediatrics) and each child will be assessed 5 times at 6-month intervals for a total of 2 years.

The investigators will collect serial hair samples at each visit, obtain anthropometric measures at yearly intervals, and also assess the child's cognitive, behavioral, social-emotional, relational, and other outcomes using bilingual parental surveys.

Parents will also provide basic demographic data, other parent- and family-related factors via bilingual questionnaires. Parents have the option of refusing to answer any question or complete the survey instruments that they are not comfortable with completing. The questionnaires that will be used in this study are the Demographics and Child Relationships Survey, the Child Opportunity Index 2.0 (SDOH), the Parenting Stress Scale (PSS), the Brief Symptom Inventory (BSI-18), the Conner-Davidson Resilience Index (CD-RISC-10), the Interfaith Spirituality Scale - Short Form (IFS-SF), the Health Mindset Questionnaire, and Parenting Styles & Dimensions Questionnaire for parents; as well as the Child Health History Survey (CHHx), the Ages and Stages Questionnaire (ASQ-3), the ASQ Social Emotional Questionnaire (ASQ:SE-2), the Speech & Language Assessment Scale (SLAS), the Child Aces & Related Life Events Scale (PEARLS 2.0), the BRIEF-Preschool Executive Functions Scale, the Positive Childhood Experiences Scale (PCEs), and the Child Flourishing Index for their child. At Study Exit, the parents will be asked to complete a very brief Study Closeout Questionnaire.

Inclusion Criteria:

1. Normal, healthy children aged 6 months to 24 months and their mothers (or father, if mother is not able to participate).
2. Living in Santa Clara County, San Mateo County, or Alameda County in Northern California.
3. Willing to give their home address (in order to receive the study kits at home).
4. Committed to regular follow-up at 6-month intervals for the full study duration of 2 years.

Exclusion Criteria:

1. Children with tinea capitis, alopecia areata, scalp eczema, dermatitis, or other scalp conditions.
2. Children exposed to systemic steroid therapy for any diagnosis in the 3 months prior to study entry.
3. Children receiving any other prescription drugs that alter HPA axis function or cortisol release, if the period of exposure is 2 weeks or longer within the 3 months prior to study entry.
4. Children with chronic medical conditions such as cystic fibrosis, sickle cell disease, asthma, eczema, or other chronic conditions.
5. Children with known developmental delay, Trisomy-21 and other chromosomal anomalies, seizure disorders, chronic pain, cerebral palsy, or other disabilities.
6. Children whose hair has received chemical exposures (e.g., dying, bleaching, chemical straightening, perming) in the 90 days prior to study entry or for 90 days before each follow-up appointment during the 2-year study period.

Normal, healthy children aged 6 months to 24 months and their biological mothers (or father, if mother is not able to participate), in order to study the impact of early social ecology on their nascent social psychology, growth, and development in early childhood.

IPD will not be shared because of proprietary methods used for analysis of hair samples.