The Enterprise is transporting its first Captain, Robert April to Babel, where he will reluctantly accept his retirement. When the Enterprise attempt to stop an unidentified vessel on a collision course with the Beta Niobe nova, the ship accidentally pass into an alternate dimension, where time flows in the opposite direction. The crew of the Enterprise rapidly begins to grow younger in age, and soon become unable to man the consoles.
The TV Archaeologist
Did You Know?
This episode is largely regarded as the "Spock's Brain" of the animated series. No reason is given as to why the crew de-age so quickly. They were only in the negative universe a few days at most. While they would de-age, it would not even be noticeable. They certainly would not have become children. See more
Captain, the flower is not the only thing on board that is growing younger.
Ship's chronometers are also running backwards. The flow of time is reversed in this universe. The longer we stay here, the younger we will become.
References Star Trek: The Empath