Fats, divided into saturated (from animal sources, such as butter and cream) and unsaturated (of plant origin, such as olive oil and seeds), are essential because, in addition to providing energy that is stored, they regulate metabolic exchange, carry some vitamins, and contribute to the formation of cell membranes of the central nervous system, brain and retina.
While carrying out important tasks, especially during growth, fat must be introduced in the right quantities, preferring unsaturated fats (too much saturated fat can cause overweight or even obese children and the emergence in adulthood of heart disease).
You should keep in mind that there are invisible sources of fat: a lot of saturated fat, for example, is "hidden" in cheese, eggs, meat, sausages etc., while unsaturated fats are found in fish, nuts and some meats.
During the first year, 85-90% of the calories taken in are used to maintain bodily functions and for growth, while only 10-15% are for physical activity. In the second half, proteins should provide 10% of the contribution of energy, carbohydrates 50% and fat 40%.