I have a 5 year old. Starting when he was 4 years old we went on 5-8 mile hikes in 3-5 hours, and he walked the entire way. Little kids can do the miles, but they need lots of little breaks. The problem with hiking with little kids is that if you are carrying them you cannot carry your gear. My wife and I are prepared to stay put rather then try to bug out if the SHTF.