We did a 7 day Galapagos Island voyage on the Isabela. This trip was always on my "bucket list." I'm not sure that the kids knew what to expect although we tried to prep them with books and videos beforehand. We so enjoyed getting so up close to all of the wildlife - especially the sea lions. I have one child who is a HUGE animal lover so the experience was even more special for him. Swimming and snorkeling with the sea lions was truly magical and we will never forget it!
I think children should be at least 7 in order to truly get the most out of going to the Galapagos. At 7, kids can sit through and get something out of the lectures as well as participate in the hikes and snorkels with out a problem. We do tend to travel a lot with our kids, and as they have gotten older we have been more and more adventurous with them. We often travel with another family that has kids the same age so the kids have play mates- and so do the adults. We look for interesting off the beaten path hotels, that are comfortable, but not fancy. We make sure there are plenty of activities that we can all do together that both the adults and the kids will enjoy. We have boys so that usually includes lots of active pursuits like hiking, biking, riding, and swimming.
We found Kristy to be hugely helpful, as would anyone, due to her extensive experience in the Galapagos. She was able to give great advice as to which itineraries we should aim for, as well as which boats and cruise companies would be ideal for us given our budget. I think without Kristy's help we would have been shooting in the dark.