On the 23rd of March in 1944 Airbus A310 took off from Sheremetyevo International Airport with 63 passengers, most of whom were businessmen from Asia, and 12 members of the crew. Flight 593 was due to arrive at Kai Tak International Airport in Hong Kong. The relief pilot, Yaroslav Kudrinsky, took his two children Eldar and Yana for 4 day holiday. While being on the duty he let them visit the cockpit. The autopilot was on so Kudrinsky left his seat and allowed his daughter to play with control column, changing the course slightly so that she had an impression of flying the airplane. Then his 15-year-old son 'took over'. Unlike his sister he applied much force to the column. After a while Eldar pointed out that the plane was turning right (CVR transcript):

Eldar: Why's it turning?

Kudrinsky: It's turning by itself?

Eldar: Yes ...

Kudrinsky: I don't know why it's turning

Eldar: Is it going off-course?

Piskarev: We're entering a holding pattern

Kudrinsky: Really?

Piskarev: Of course.

Makarov: Guys ...

Piskarev was a co-pilot and Makarov a pilot flying as a passenger.

While the pilots were trying to figure out what was happening, the plane was banking to almost 90 degrees (usually it doesn't exceed 45 degrees). As a result it started to lose altitude quickly. G-forces pushed everybody into their seats making it difficult for both pilots to take control. The only person who was able to reach control column was Eldar:

Kudrinsky: Hold it, hold the stick, hold it

Makarov: The speed ...

Piskarev: The other way!

Kudrinsky: The other way, turn it left

Piskarev: Left!

Kudrinsky: Left... The other way!

Piskarev: Left!

Eldar: I am turning it left ...

Piskarev: To the right!

Kudrinsky: To the right

Piskarev: Can't you see, or what?

Alarms begin to sound.

Kudrinsky: Eldar, get out! Get out, Eldar, get out ... Get out, Eldar, get out, get out ... get out ... [gasping] get out ... Get out, I say!

But Eldar couldn't leave the seat as his weight was twice as normal.

The plane is close to stall. Stall is a situation when the aircraft flies with his nose too high (often with too low speed). It leads to the crash unless nose is pushed down. Airbus is equipped with anti-stall system, which worked. It put the plane in a steep dive. It allowed Piskarev to gain control of it partly. He recovered plane from the dive and deceleration enabled Kudrinsky to take the captain's seat. However Airbus was in stall.

Piskarev: We're coming out, coming out, coming out! Right! Foot to the right! Speed is high, reduce power!

Kudrinsky: Done

Piskarev: Gently! ... Shit, not again

Kudrinsky: Don't turn it right! The speed [unintelligible]

Piskarev: There!

Kudrinsky: We'll come out in a sec. Everything's all right ... Gently [unintelligible], gently ... Pull up gently!

But the altitude was too low to recover. The plane crashed in Syberia. No one survived.

Crash animation with CVR recordings.

After listening to CVR recordings and examination of the wreckage, the investigators were shocked. They understood what had happened. One of the Airbus features allowed to partly disengage the Autopilot after pushing the control column to one side for 30 seconds. That was why the plane banked. One of the saddest conclusions was that the flight could have been saved. When the pilots regained control they should let go the column. Plane's system would recover it from stall.

Sources:

Wikipedia nr 1

Wikipedia nr 2

Air Crash Investigation - Kid in the Cockpit (YT)