When an athlete is new to jumping and landing, the most consistent error is that the knees collapse or turn inward upon take off, landing or both. 

If this is happening with your group, know that this is common. 

Cue them to keep the knees out at all times to mitigate the collapsing of the knees.

The freeze landing just means that when the athlete hits the ground, we want zero additional movement.

If they need to take a few seconds between reps to settle and then jump again, that is fine.

Lastly, upon landing we want to make sure the swimmer remains upright. Maintaining control throughout the entire repetition is vital.