I did this with my 10 year old and my 6 y/o (who are somewhat adventurous). We had a terrific time. The kids loved it so much they demanded doing ziplines later in the trip with a different company in Vulcan region. The guides were great, bilingual and they went with my 6 y/o when she didn't want to go alone. As the previous reviews said, a great part of this zipline trip is the swim half way through at the montezuma waterfalls. There are some fun 10-15 foot jumps off rocks you can do and also a rope swing. Beautiful, fun and refreshing.
This was a highlight of the trip for my kids (and admittedly for me too :))