The "slow-to-warm-up temperament" is a personality style often observed in children. Individuals with this temperament may initially react with caution or hesitation in new situations or around unfamiliar people. They typically take time to adjust and may need support to feel comfortable before fully engaging. This temperament is one of the three main categories identified by Alexander Thomas and Stella Chess in their research on child development. Children with a slow-to-warm-up temperament may show a gradual increase in comfort and participation as they become more familiar with their environment, often displaying a calm and observant nature.