Your airline should give you a blank Customs Declaration form 6059B. Only one Customs Declaration is required for a family traveling together.
A visa does not guarantee entry into the United States, but allows a foreign citizen coming from abroad to travel to a U.S. port of entry and request permission to enter the United States. The Department of Homeland Security, U.S. Customs and Border Protection (CBP) officials have authority to permit or deny admission to the United States, and determine how long a traveler may stay. At the port of entry, upon granting entry to the United States, the Customs and Border Protection officer will determine the length of stay permitted. Previously, travelers received a paper I-94 (record of admission) with this information. This process is now automated. The traveler will be provided with a CBP admission stamp on their travel document that shows the date of admission, class of admission, and admitted-until date. If a traveler needs a copy of their I-94 for verification of alien registration, immigration status or employment authorization, it can be obtained from www.cbp.gov/I94. You can review information about admission on the CBP Website. The Department of State’s Consular Affairs website has more information about duration of stay.