The brain requires adequate energy to function well and this can be provided with good nourishment through good food intake and regular physical activity. When your child is involved in strenuous mental activities such as exam preparations, planning for extra curricular activities, then your child will require extra energy.
Along with regular intake of healthy food, there are a few main foods which you need to include which will provide minerals such as zinc, lecithin, manganese, omega 3 fatty acids and Vitamins such as Vitamin E.
Good sources of these nutrients are whole wheat products, brown rice, oats, soya beans and legumes, eggs, milk, curds, cheese(yes it is safe to give cheese as a snack), nuts, unrefined vegetable oils. Flax seeds and fish too are good sources of omega 3 fatty acids.
Besides these nutrients, adequate sleep and exercise is required. Exercise helps in stimulating fresh oxygen to the brain and sleep helps to relax and unwind the brain.
Involve your child in brain racking activities such as chess and also make your child do puzzles, crosswords and memory games.