In the first decade of life, children become bilingual in different language learning environments. Many children start learning two languages from birth (Bilingual First Language Acquisition). In early childhood hitherto monolingual children start hearing a second language through daycare or preschool (Early Second Language Acquisition). Yet other hitherto monolingual children in middle childhood may acquire a second language only after entering school (Second Language Acquisition). This Element explains how these different language learning settings dynamically affect bilingual children's language learning trajectories. All children eventually learn to speak the societal language, but they often do not learn to fluently speak their non-societal language and may even stop speaking it. Children's and families' harmonious bilingualism is threatened if bilingual children do not develop high proficiency in both languages. Educational institutions and parental conversational practices play a pivotal role in supporting harmonious bilingual development.

This Element first reviews the limitations of the concepts of problems in childhood. It proposes a universal, comprehensive, and longitudinal conceptual framework of problems in childhood, their differential context, and their cyclical effects. Based on the linkages identified in the children's problems, they are divided into three levels, primary, secondary, and tertiary. The Element then reviews the concepts and the limitations of the prevalent service delivery approaches of child welfare, protection, and justice, because of which these services have not helped to break the cycle of problems in childhood. The Element identifies the rights-based comprehensive, preventive, and systemic approach for child welfare, at primary, secondary and tertiary prevention levels, in order to break this cycle of problems. Finally, the Element goes into details of the tertiary prevention level integrated service delivery for children facing socio-legal problems.

In this Element, I first introduce intelligence in terms of historical definitions. I show that intelligence, as conceived even by the originators of the first intelligence tests, Alfred Binet and David Wechsler, is a much broader construct than just scores on narrow tests of intelligence and their proxies. I then review the major approaches to understanding intelligence and its development: the psychometric (test-based), cognitive and neurocognitive (intelligence as a set of brain-based cognitive representations and processes), systems, cultural, and developmental. These approaches, taken together, present a much more complex portrait of intelligence and its development than the one that would be ascertained just from scores on intelligence tests. Finally, I draw some take-away conclusions.

The focus of this Element is on the environment and how it is implicated in children's development.A very broad array of social and physical features connected to children's home life and to the neighborhoods where children live, including multiple aspects of parenting, housing characteristics and the increased prevalence of media in daily life are addressed.Attention is also given to the broader social, economic, and geographic contexts in which children live, such as neighborhood surroundings and conditions in less developed countries.There is a focus on how various aspects of the home context (e.g., crowding) and key parental characteristics, such as mental illness and substance abuse problems, affect the behavior of parents. Consideration also given to how various forms of chaos and instability present challenges for parents and children and how those circumstances are implicated in both children's development and caregiver behavior.

Gender is a highly salient and important social group that shapes how children interact with others and how they are treated by others. In this Element, we offer an overview and review of the research on gender development in childhood from a developmental science perspective. We first define gender and the related concepts of sex and gender identity. Second, we discuss how variations in cultural context shape gender development around the world and how variations within gender groups add to the complexity of gender identity development. Third, we discuss major theoretical perspectives in developmental science for studying child gender. Fourth, we examine differences and similarities between girls and boys using the latest meta-analytic evidence. Fifth, we discuss the development of gender, gender identity, and gender socialization throughout infancy, early childhood, and middle childhood. We conclude with a discussion of future directions for the study of gender development in childhood.

Natural selection has operated as strongly or more so on the early stages of the lifespan as on adulthood. One evolved feature of human childhood is high levels of behavioral, cognitive, and neural plasticity, permitting children to adapt to a wide range of physical and social environments. Taking an evolutionary perspective on infancy and childhood provides a better understanding of contemporary human development, predicting and understanding adult behavior, and explaining how changes in the early development of our ancestors produced contemporary Homo sapiens.