|Not only do children walk "slower" than|
adults, they prefer to wander and explore
Compared to adults, kids can't walk as far, they can't walk as fast, and they will grow bored more quickly. Every step we take requires three for them. In addition, early walkers, up to 2 years of age, prefer to wander than to "hike." Pre-school kids will start to walk the trail, but at a rate of only about a mile per hour. With stops, that can turn a three-mile hike into a four-hour journey. Kids also won't be able to hike as steep of trails as you or handle as inclement of weather as you might.
This all may sound limiting, especially to long-time backpackers used to racking up miles or bagging peaks on their hikes, but it's really not. While you may have to put off some backcountry and mountain climbing trips for a while, it also opens up to you a number of great short trails and nature hikes with spectacular sights that you may have otherwise skipped because they weren't challenging enough.
So sure, you'll have to make some compromises... but the payout is high. You're not personally on the hike to get a workout but to spend quality time with your children. And they'll always get older and be able to go farther.
Be careful, though, what you wish for. With older teenagers, the problem becomes quite the opposite of toddlers - keeping up with their high metabolism.
Read more about day hiking with children in my Hikes with Tykes guidebooks.