I found this, and the last line of what I copied/pasted covers your question:
http://www.twc.state.tx.us/ui/lablaw/cllsum.html
Under the 4th section from the top, it says:
Hours of Employment under State and Federal Law
Texas State Law:
A child 14 or 15 years of age may not work more than eight hours in one day or more than 48 hours in one week. A child who is 14 or 15 years of age and is enrolled in a term of a public or private school may not work between the hours of 10 p.m. and 5 a.m. on a day that is followed by a school day or between the hours of midnight and 5 a.m. on a day that is not followed by a school day. A child who is 14 or 15 years of age and is not enrolled in summer school may not work between the hours of midnight and 5 a.m. on any day that school is recessed for the summer.
Federal Law:
Under the Fair Labor Standards Act (FLSA) a child 14 or 15 years of age may not work outside of school hours, may not work more than three hours on a school day or 18 hours during a school week, and may not work more than eight hours on a non-school day or 40 hours during a non-school week. Furthermore, a child 14 or 15 years of age may work only between 7 a.m. and 7 p.m. during the school year. Between June 1 and Labor Day, a child may work between the hours of 7 a.m. and 9 p.m.
A child 16 or 17 years of age have no restrictions on the number of hours or times of day they may work.