My young nephew often flew with me in the right seat as a passenger when I did freight runs or positioning flights (single pilot) in a Twin Otter. By the time he was eight, he could do a quite a good job of maintaining altitude by looking at the altimeter and attitude indicator - he wasn't tall enough to see out over the glareshield.
When he was nine, my wife and I took him with us on an Air Canada flight. He asked if he could see visit the pilots, and in due time, the flight attendent fetched him and took him up front.
When she brought him back a few minutes later, she was laughing... apparently the Captain had asked him if he knew what altitude we were flying at, and he looked at the altimeter and then replied "You're 50 feet low". That brought a quick end to his visit to the pilots.