Twilight on the Trail (1941)

Rustlers are raiding in Antelope Valley and Jim Brent, owner of the Circle Y Ranch, sends for eastern detectives to catch them. The detectives arrive and, much to the disgust of Brent, his daughter Lucy, and the other cattlemen, they turn out to be a trio of foppish dudes. But, in reality, they are 'Hopalong" Cassidy and his sidekicks, "California" Carlson and Johnny Nelson, dressed in order to throw the outlaws off their guard...and also do the same for the kids in the front row.