Children between 2 and 11 years old can only travel accompanied by an adult. Simply indicate that there is a child before clicking on "search and purchase".
See what the rules are for unaccompanied minors*:
Available during the online purchasing process, at the Azul Center and at the airport.
*In compliance with the Statute of Children and Adolescents, section 3, article 83, paragraphs 1 and 2.
No problem, you can include more pounds at the airport during check-in. But attention, if the weight of checked baggage exceeds 23kg will be charged the excess of luggage.