NASA Johnson Space Center
Houston, TX 77058
Be sure to include a self-addressed, stamped envelope for them to use to respond to you and also give it some time for they are really busy.
Also, there is an Ask An Astronaut website, but beware about only 10 % of submitted questions are responded to at: http://www.discoverspace.org/askastronaut_current.cfm
The StarChild site is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA/GSFC.
The StarChild Team
StarChild Graphics & Music: Acknowledgments
StarChild Project Leader: Dr. Laura A. Whitlock
Responsible NASA Official: Phil Newman