Totally agree! Invest the $10/ticket for Early Board Check-in. That will guarantee you all to be in Group A. Each ticket will be assigned a number. At the gate there will be lines A, B, C. You will line up in group A in numerical order. You will be able to sit together, keeping in mind most SW flights are configured 3/2 (3 seats one side, two seats across the aisle )
Additionally, maybe someone can answer what is the age of children for "pre boarding with small children."