There is a whole debate to be had about whether that's the right thing to do. I can see competing views on that. However, nothing in federal law or Texas law makes it illegal to discriminate against an employee because his/her marital status or because of his/her status as a parent or being childless. In short, whether it is the right or wrong thing morally, it's not illegal.
If the employee is paid at least minimum wage for time worked, the the employer is not violating the minimum wage laws. However, employment discrimination based on marital status is a separate thing from wage and hour laws. Of course, since Texas does not appear to make it illegal for employers to discriminate on the basis of marital status, it ultimately leads to the same conclusion.