luke shambrook , 11 , was found after he went missing on good friday .
he went missing in lake eildon national park - north-east of melbourne .
his family had taken him to the park since he was just one year old .
` every year he 's been up and down the hills , ' his dad tim said .
the autistic boy was found on tuesday by a police helicopter .
doctors are amazed at how well he is doing considering his four-day ordeal .
the boy was suffering from dehydration , hypothermia and exhaustion .