Studies have shown association between cognitive function and some micro-nutrient like zinc, folic acid, omega-3 fatty acids, vitamins B12 etc fortunately, most of baby cognitive functions are acquired naturally.
If in an iodine-deficient area (and there are many all over the world), and iodized salt is not available or not actually contain enough iodine, iodine is critical for neurological development.
A lack of folic acid, iodine and poor thyroid function have been shown to be related to poor development, but then enough food in general is important for neurological development. Much neurological development depends on adequate stimulation (and television doesnt provide it- it has to be from another human- see Scientific American within the last year) and of course good genetics.
Attached the papers showing fish three times per week to result in higher functioning three year olds. (But it could be smart people eat fish! :)
In one test: One third of nutritional supplements had NONE of the ingredient that was labeled on the bottle of nutritional supplements. John Oliver reports on how lobbying by paying off senators has resulted in no regulation of nutritional supplement companies- they need not approval, and dont have to prove safety of the product before marketing it. If interested, watch the link below
Actually, for fetal neurocognitive development very important role plays mother psychoemotional status during pregnancy and how the mother is trying to help baby to develop while she or he is inside the uterus (music, reading books, touches, stimulation and etc.)