When getting quotes for your child(ren) only, enter the child's gender and birth date in the "Applicant" or first row. Additional children should be entered below in the "Child" rows, but not the "Spouse" row.
However, many health insurance companies require one policy per child. So if you have more than one child, try entering just one child to see a larger selection of plans and prices. You are free to apply for each child separately.
