Hey Pedro, I just came across some information that can give you exactly what you've been looking for. I want you to click the link here: http://dept.houstonisd.org/backtoschoolfest/index.html
This is the announcement from the City of Houston: "Back to School Fest on Saturday, August 11, 2012, 8:00 a.m. - 12:00 p.m., at the Reliant Center.Just a few of the many attractions available will be games for children, health screenings, and free immunizations, school uniforms, and school supplies. District representatives will also be on hand to provide information to parents on the many school options available. Please join us for a full morning of family fun! Veterans and families are welcome."
You can check with the assistance ministry that services your zip code (i.e. Memorial Assistance Ministries, West Houston Assistance Ministries, Katy Christian Ministries, etc.). You can also apply for assistance with the Y's Operation Backpack http://www.ymcahouston.org/operation-backpack/contact/.
Hope this helps!
Just came across this link for school supplies, free haircuts, and immunizations.