This was AMAZING, I would highly recommend it to anyone! In addition to zip lining, you also get to do a 'Tarzan swing' on a rope off a huge ledge, and repel down a rope (really, slide down it) and then climb a rope ladder up a tree. Was definitely terrifying at moments and got my legs shaking, but the guides were very knowledgable and knew how to take care of us. There were a few kids on the tour - probably 6 or 7 - and they did just fine, so seems very safe for a family. One caveat I will say is if you are scared of heights and need reassurance, this may not be the company for you. Our guides joked a lot and were very entertaining, but they liked to poke fun at guests in ways you might not find amusing if you're genuinely terrified. We all found it hilarious, and maybe if you speak to them beforehand about your fears they'll act differently - not sure. But something to consider if you're getting way out of your comfort zone.
Otherwise, we really enjoyed this tour and would 100% do it again and recommend it to any friends coming to Monteverde.