We bought adjustable latches with a little extra metal bit where you can lock them. The problem, however, is that the range of adjustment is limited by the lock attachment point. Eventually, the screw bumps into the lock attachment and you cannot adjust the lock any smaller. If they had offset the lock attachment point, you could adjust the latch the full length of the threading.

Because we needed some smaller latches, we had to use a hacksaw to cut off some of the threads. Now it can be screwed down to its smallest size and our baby chickens are secured in their tractor.