Good on you. This is definitely a case of "product of their enviroment". You should be so proud of your kids, and yourself. An experience they will never forget. What are their ages, and what was the longest hike you did together before this one? This sure brought back great memories of times I spent hiking with my father, rest his soul.
We did most of the JMT in 2008 when they were just 10. Had to bail at Taboose Pass when blisters became painful and overall motivation was running low. Before that they never did more than short day hikes, so that year was pretty rough.
Next summer at age 12, they'll be seasoned Sierra veterans and that "youngest hikers to do the Muir Trail Yo-Yo" goal still stands. I think it's 90% certain we'll be back and hopefully this time around we'll really grab our food cache at the Portal store and head right back up. We may even bring a fishing rod and do things we cut out this summer to save a few ounces from the packs, but really enjoyed in 2008, like here at Evolution Lake