The advisory from the FDA and EPA says it's okay to serve your child two child-sized servings a week of any fish and shellfish, other than the four you shouldn't serve at all: shark, swordfish, king mackerel, and tilefish. (See special restrictions on canned tuna below.) A child-sized serving is 1 ounce of fish for 1- and 2-year-olds; 1.5 ounces for children ages 3 to 6; and 2 ounces for a child over age 6.