Taking them out for fresh air

We were told by our breeder to not let the cats outside as they would turn into wild cats and destroy the native fauna. Buddy and Macaroon are strictly indoor cats but I believe they should be entitled to outside time and fresh air. We haven't found a suitable cat run for our background as it is quite small and feel nervous about letting out alone. Today we bought a harness and lead to take them for mini strolls around our yard. We tried them out this afternoon and the cats were quite curious! After 10 minutes they both requested to go back indoors.