To stay safe, even fit, experienced trekkers need a crash course on trail hiking in the mountains and jungles of Hawaii. First of all, even popular trails are going to have rough patches. Bring retractable hiking poles and expect slippery rocks, undulating surfaces, and steep portions where hands will be required.
Greenery alongside trails can disguise steep drop-offs. Don't step off into the snarls, and watch the kids.
If you lose the trail, or the going gets gnarly, turn back to a known point. Even hunting dogs with big bazooka noses get lost in Hawaii. Don't use GPS or a map to try to reach a destination cross country. Stay on the trail and follow your feet. If it's possible to walk someplace in Hawaii, someone has done it before you. Plant life will swallow you whole. Cracks in the earth, created by volcanic activity and hidden by flora, are lethal booby traps.
Speaking of hunting dogs: Always yield the trail to a wild pig.
Stream crossings can be mellow one minute, and rise up the next. Cloud bursts may happen inland when it's sunny where you are. If you find yourself on the wrong side of a swift stream, wait it out. The water will subside. Don't cross.
BTW: Though this spillway makes it easy to go shoeless, you might as well keep them on , since crossings can be numerous (and the water will clean the mud off!). No sense in bringing waterproof boots, since you are likely to dunk them higher than ankle deep.
Travel in pairs, or at least let someone know you are headed out. Make sure to allow enough daylight for your return.
Don't even think about rock climbing. Almost all cliffs and mountainsides are very unstable. Many trails have drop-off hazards.
Keep in mind that hiking times for a given distance will be about double in Hawaii, due to poor footing—and stopping to gawk at the scenery.
Trail conditions can change overnight due to landslides, tree-falls, and erosion. If you feel the trail ahead is unsafe, then it is. Turn around. Many people 'go for the gusto' on Hawaiian trails thinking they are in some sort of adventure Disneyland. Common sense is your friend.
No poisonous snakes or spiders to fret about, but muddy surfaces are common. Wear dark shorts and don't forget those hiking poles.
Equip your daypack with all the essentials and bring it with you even if you're going on a very short hike. You might start out on a little exploration jaunt and be drawn in farther than you intended.
Trailblazer guides are full of parking and trail directions, safety tips, and the specific hazards that may be present for each hike. Virtually every danger is avoidable.