Had a quick search, gets a brief mention in this article together with another one halfway down the page.
National Park vanishings | Chasing The Unknown (wordpress.com)
Keith Parkinsin was only 2 years old when he disappeared near Oregon’s Umatilla National Forest in 1952. Luckily he was found alive less than a day later, but it cant be ignored that he was found a staggering 12 miles away. An analysis determined that he would have had to traverse water, fences and not one but TWO mountain ranges. At 2 years of age, this feels a stretch.
A 2-year-old boy vanished in Yosemite National Park in 1957. He was found after hundreds of people and tracking dogs had been looking for him. He was found missing his pants and had somehow managed to climb up a 3000ft high rock face. No one was ever able to explain how he got up there but luckily survived with just dehydration.