Some suggestions:
Lava tubes vary significantly and can also breakdown.
Instead:
Lava tubes vary significantly and can also break down.
Any cave can have loose boulders that can be knocked over by a careless explorer. Be careful!
Boulders are not necessarily knocked over (to me this means going from upright to prone) but are knocked loose. Which means then they roll or fall someplace else, and that may endanger the group. Perhaps instead:
Any cave can have unstable boulders that can be knocked loose by a careless explorer. Be careful!
Some caves have the potential to flood during times of high water or flash flood. Your guide should be aware of the flood risks in the cave that you are exploring. Additionally, you may wish to monitor the local weather conditions and precipitation history before going caving.
Perhaps instead:
Some cave passages can flood during times of high rainfall, flash flood conditions, or high water levels. Your guide should be aware of the flood risks in the cave that you are exploring. You should check the weather forecast and recent rainfall before the youth group enters any cave that is prone to flooding.
Hope this helps!
Cheryl