It would be best if you discuss this with your pediatrician.
Personally, I would recommend all three of you get it since you will be traveling during flu season. The American Academy of Pediatrics now recommends influenza immunization for all children 6 months through 18 years of age, as well as household contacts of children younger than 5 years. See their influenza recommendation for 2008-2009:
http://www.cispimmunize.org/ill/Flu/Influenza%20Recommendations.pdf