This is sexist against fathers and therefore unconstitutional.

Bill text:

Sec. 545.429. USE OF HIGH OCCUPANCY VEHICLE LANE BY CERTAIN OPERATORS. (a) Subject to Subsection (b), a female operator of a motor vehicle who is pregnant or is a parent or legal guardian of another person is entitled to use any high occupancy vehicle lane in this state regardless of the number of occupants in the motor vehicle.

Texas Constitution:

ARTICLE 1. BILL OF RIGHTS

Sec. 3a. EQUALITY UNDER THE LAW. Equality under the law shall not be denied or abridged because of sex, race, color, creed, or national origin. This amendment is self-operative.

What this would actually do (once the test case ruled that it would have to apply to fathers too) is destroy HOV lanes entirely by making everybody able to use them, since the state would have the burden of proof to show that the driver has never had children.