“Many of the things we need can wait; children cannot. Now is the time: their bones are forming, their blood is too, and their senses are developing. We cannot tell them ‘tomorrow;’ their name is today.”

—Gabriela Mistral

The first 1000 days of life span from conception to the 2^nd year of life have been demonstrated to be a decisive period in human development. During this period, human beings grow at an incredible speed, laying the foundations for physical, emotional, and cognitive health for life. The decisions made regarding this person, from the moment of pregnancy, not only affect their current health but also define their future health. This stage can unfold naturally, with processes taking place despite any deficiencies or hardships. However, it is through education and responsibility that it becomes possible to modify these determinants. The first 1000 days are one of the most vulnerable stages of life; therefore, adequate nutrition, basic healthcare, and a stable emotional environment can make a big difference¹-⁶.

From a biological perspective, the development of the organism, particularly the brain, is remarkable; neuronal connections grow at an unprecedented rate, and the way a child experiences the world during this stage is fundamental to their capacity to learn, think, and establish relationships with others⁷,⁸.

This is the first great opportunity: early motivation. Children interact with their mother, play with their caregivers, and if this takes place in a safe and welcoming environment, they will have greater and better chances of developing cognitive, linguistic, and emotional skills that will last a lifetime. These interactions influence not only their quantity but, above all, their quality. Societies that invest in education, healthcare, and family support can ensure a substantial change in potential, transforming reality and guaranteeing equality of opportunities from the very beginning. The motivation of knowing they can change their environment is a lesson that will shape the way they attend school, navigate society, and understand that they are not destined to a future bound by the same conditions⁹.

Parallel to this process, physical and emotional development play a fundamental role. To achieve this, breastfeeding must be exclusive during the first 6 months of life, ensuring that the newborn receives all necessary nutrients and immunoglobulins, as well as affection and attachment. In this regard, we must recognize that achieving this goal requires supporting mothers through maternity leave and breastfeeding facilities in their workplaces¹-⁴. Failure to guarantee these rights increases the risk of malnutrition and preventable diseases.

This supplement of the Boletín Médico del Hospital Infantil de México addresses the subject of child development, focusing on the evaluation and early detection of possible disorders. In addition, it offers an updated and highly relevant review for all countries in the region, describing the screening tests available in the Americas, the policy-making process in Peru regarding child development evaluation, and the experience of validating a Mexican screening test in Colombia. A series of studies highlight the Mexican effort to establish a diagnosis of developmental levels through a screening test developed by Mexicans for Mexican children and children worldwide. This tool, the Child Development Evaluation or CDE test¹⁰, results in a color-coded system that prompts families and healthcare providers to request confirmation and take timely action. Validating, implementing, and disseminating the test across various settings and with different stakeholders, including through telemedicine, was necessary. Furthermore, this supplement includes the story of the unwavering commitment of the Developmental and Behavioral Pediatrics Service at the Hospital Infantil de México Federico Gómez, led by Antonio Rizzoli, to the development of Mexican boys and girls.

Public policy has far-reaching implications in this regard. Improving the quality of maternal and child health programs, nutrition, immunizations, and promoting safe spaces is an investment not only in the child but also in the future of society. The cost of not intervening rapidly is high, as affecting individual development impacts the collective potential of the country.

Opportunities should also focus on emotional health, as research has shown that this period represents a unique window to build strong relationships that form the foundation of long-term emotional well-being. Children who experience secure attachment, who are hugged and listened to, are more emotionally stable, better able to cope with stress, and more likely to develop positive relationships in the future. These actions, which align with the original definition of biopsychosocial health, are achieved through community programs and family support strategies that receive adequate resources to establish these connections and foster prosperity⁹.

Today, poverty, violence, and lack of resources can hinder this process. However, early intervention can generate decisive changes. In the context of global inequality, opportunities to improve the lives of the most disadvantaged children are more urgent than ever. All children deserve to feel safe and cared for, regardless of their social or economic background.

Every child is a promise for the future. The first 1,000 days are undoubtedly a great opportunity because by changing the life of one child, we can change the destiny of society. The decisions we make now will shape the world of tomorrow.