I suppose just for the marquee value of the names of Mitchum, McCrea, and Ladd Young Guns Of Texas cast them in the leads. But it's not the people with those names you're familiar with. Young Guns Of Texas stars James Mitchum, Alana Ladd, and Jody McCrea and is set in post Civil War Texas where some former Confederates have robbed a payroll. What would have been an act of war now makes them outlaws.
Mitchum and McCrea team up with Gary Conway who is another young gun looking for the payroll. But Mitchum mixes some pleasure in it when he also runs off with Alana Ladd daughter of the local rancher Robert Lowery who really doesn't like Mitchum. He sics his foreman on Mitchum, but Mitchum kills him. Now Lowery gets a posse going after the young guns.
McCrea is the son of the local preacher Chill Wills who married the couple and Wills joins them.
Did I forget to mention that the payroll robbers, the young guns, and the posse are all riding into Apache territory? Some honeymoon Mitchum and Ladd are going to have.
No credit was reflected on those great movie names by their kids appearing in this western. Yes it's as dumb as I've described it.