No Deposit, No Return (1976)

Mischievous youngsters Tracy (Kim Richards) and Jay (Brad Savage) quickly grow tired of staying with their dull but wealthy grandpa, J.W. Osborne (David Niven). So they devise a brilliant scheme in hopes of funding a plane trip to China to visit their mom. The kids enlist bumbling burglars Bert (Don Knotts) and Duke (Darren McGavin) to kidnap them, then demand a huge ransom check from Osborne. Unexpectedly, the children and the crooks bond and begin forgetting all about their arrangement.