The Sugarland Express.

Married small-time crooks Lou-Jean and Clovis Poplin lose their baby to the state of Texas and resolve to do whatever it takes to get him back. Lou-Jean gets Clovis out of jail, and the two steal their son from his foster home, in addition to taking a highway patrolman hostage. As a massive dragnet starts to pursue them across Texas, the couple become unlikely folk heroes and even start to bond with the captive policeman.