Resources, Guidelines, Ideas for Training Program for Children

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Hi- I'm guessing there are people in this forum who are knowledgeable about training/ exercise programs for children. I would like to design a program for my children, aged 4-14, to prepare to hike up Mt. Marcy in New York in October. It's a 14 mile hike. Last summer they did a 7 mile hike up Hearney Peak in South Dakota with no problem. They are fit kids, but I'm not sure of how to safely plan such a program. My idea is to do indoor rowing on days when it is raining (not very often), go on bike rides about twice a week (the youngest will ride on a trail-a-bike), run on the trails in our woods a couple of days a week, and go for a hike as a family once a week. The kids enjoy each of these activities. I'm not sure if this is too much, and if there is anything else I should include. Referrals to any resources on this subject will be appreciated. Thanks!