The first 1000 days spans from the child's birth to their 2nd year of age, where they develop and learn rapidly based on their environment. With focus on nutrition, the child's immune system and brain must develop well to prepare for the challenges growing up.
A strong immune system is vital as this would help protect the child from diseases and illness. Once strong enough, the child's body can focus on developing and strengthening itself. Immunizations through vaccination will also help the child's immune system, along with breastfeeding which will fill and develop the child's gut microbiome (found to strengthen the immune system), as well as strengthen the mother and child bond. This bond is also another form of nutrition for the child, allowing them comfort and care which also positively affect their development in the long term.
Along with this, the brain is rapidly adapting and making sense of the world, fixing and adjusting reflexes to ensure preparedness for further growth. This includes neuromuscular connections such as basic walking, grasping, and reacting. Memories are also beginning to form and once again, the parent-child bond is strengthened with interaction and physical affection with the child. Language learning has also begun and what the child hears in their first 1000 days help improve their ability to learn languages along with other topics. Being exposed to a variety of information and also music also help support the brain's development. Directly, nutrition from foods that contain vitamin B12 and folic acid can further improve neurological development.
As already mentioned, care and affection also acts as nutrition to the child affecting their psychological development in the early stages of life. Insufficient or incorrect nutrition of the psychological sort can severely impair the child's ability to learn and function socially, especially in their developing years which can carry on into adulthood if not corrected. As such, the focus on these three targets of nutrition can provide significant support to the child's development in their early years until their later ones.
References:
Pregnancy births & baby. (2019, December). The first 1,000 days. Retrieved from https://www.pregnancybirthbaby.org.au/the-first-1000-days#:~:text=The%20first%201%2C000%20days%20refers%20to%20a%20child%27s,body%20and%20immune%20system%20grows%20and%20develops%20significantly.