Again, this will be super personal to your family and your child's personality. My first would happily have been carried until he was six if I let him; my next, bounding around independently from about 18 months, never wanted to be carried until he literally fell asleep! Generally speaking, all things being physically well with your child, as they approach between 3 to 4 years old, you should encourage them to undertake short hikes completely on their own.