Omega-3 fatty acids are essential fatty acids that must be consumed in the diet. Adequate consumption of omega-3 fatty acids is vitally important during pregnancy as they are critical building blocks of fetal brain and retina. Omega-3 fatty acids may also play a role in determining the length of gestation, preventing perinatal depression, and helping with emotional stability. The most biologically active forms of omega-3 fatty acids are docosahexaenoic acid and eicosapentaenoic acid, which are primarily derived from marine sources such as seafood and algae. Recent surveys, however, indicate that pregnant women in the United States and in other countries eat little fish and therefore do not consume enough omega-3 fatty acids, primarily due to concern about the adverse effects of mercury and other contaminants on the developing fetus.

Seafood can also contain organic mercury and other harmful which could be harmful to the growing fetus. For this reason, the FDA/EPA recommends limiting fish consumption to 2 servings (approximately 340 g or 12 oz of seafood) per week.
Omega-3 fatty acids seem to be important during lactation as well for lactating women who received 200 mg of DHA per day for 4 months.

These links also have good information:

Omega-3 Fatty Acids
Omega-3 Fish Oil and Pregnancy
Good Fats vs Bad Fats

Children – Raise Healthy Eaters

Children 2-3 years old get 433mg of DHA/EPA with a minimum of 145mg of DHA, 4-6 years old get 600mg of DHA/EPA with a minimum of 200mg of DHA and 7 years and older including adults get 650 combined with a minimum of 220 DHA.

Be cautious when choosing nutritional supplements, many are not regulated by the FDA.
We have a reliable source for Prenatal DHA
We recommend the CustomeRx for children. They are reasonably priced and tasty. Two locations Eastside and Westside.