Don't Be a Baby is the first part of episode 20 in season 2 of Dexter's Laboratory, which first aired on November 26, 1997. In this episode, Dexter and Dee Dee try to make themselves older to go see an R-rated movie.
Mom and Dad are sitting on the couch and looking through a photo album at pictures of Dexter and Dee Dee when they were babies. Dexter and Dee Dee then come in asking their parents for money to see an r-rated movie. Their parents won't let them see the movie, pointing out that they're too young for it, but their dad promises that they can see it when they're a little older.
Hearing this Dexter drops the subject and returns to the lab with Dee Dee where he reveals the accel-ager, a giant machine linked to two hourglasses. Before entering the machine he warns her not to trip over two specific wires, which she then does and then mixes them up plugging them back in. This causes the machine to malfunction and when Dexter and Dee Dee come out they are still the same age. Realizing something must have gone wrong Dexter goes to get his tools only to notice that Monkey and Computer have become babies. He then rushes downstairs and sees that both their parents have been turned back into diaper wearing babies exclaiming that everyone in the world has been turned into babies before subsequently passing out on the spot.
Dee Dee on the other hand is excited about the turn of events and picks their baby parents, holding them in her arms. She then chastises her brother when he considers still going to the movies as they are technically older than their parents at the moment. Dexter agrees to stay and help take care of the babies which Dee Dee scoffs at saying that boys don't know how to take care of children. He attempts to prove her wrong by asking to hold Mom only to end up dropping her and cause her to start crying. Embarrassed he rushes back to the lab to fix the machine.
While he's doing that Dee Dee manages to calm Mom down by giving her a bottle, which is then quickly knocked away by Dad making her start to cry again. She then gives her a pacifier which makes her stop and calls Dad over to apologize. Instead he hits Mom and Dee Dee picks him up telling him to stop being a stinker. She sniffs the air and realizes that his diaper needs changing. Dee Dee then sets him down on the floor and proceeds to change his diaper, afterwards holding up the dirty diaper which has a large brown spot on the seat. She puts a new diaper on him and sets the two of them on the couch and attempts to sing them to sleep with a lullaby. However Dee Dee is so tired she ends up putting herself to sleep and the babies go off on their own.
Unbeknownst to Dexter the two of them enter the lab where Dad ends up tormenting Mom using a moving conveyor belt. Some time later Dee Dee wakes up and realizes that Mom and Dad are missing. She tells Dexter and he gets angry with her for losing them. The two of them then end up searching the whole house and lab before finding both babies asleep on Dexter's bed. They quietly tip toe past them into the lab and enter the now fixed accel-ager which turns everyone in the world back to their proper ages. The next morning their parent wake up in Dexter's room. Dad comments on how refreshed he feels while Mom complains that she doesn't feel so good.
Dee Dee: Dad stop being a stinker!
(She picks Dad up and then sniffs the air smelling something stinky)
Dee Dee: Eww, speaking of stinky...time to change your diaper.
(She then sets Dad on the floor and proceeds to change him. Afterwards she holds up the dirty diaper which has a large brown spot on the seat)
Dee Dee: That's better.
(She finishes taping the new diaper on)
Dee Dee: Now a little powder...
(She then sprinkles a large amount of baby powder which makes Dad cough)