Many fans have criticized the writers for letting Goten and Trunks remain children in Dragon Ball Super. That's probably one of the reasons why they don't have much screen time, plus they're busy fooling around and don't practice much. Fans were fed up with Dragon Ball sidelining the series' most important characters, but in Dragon Ball Super: Super Hero, Toriyama fixes that.
In Dragon Ball Super: Super Hero, Goten and Trunks from two young Saiyan warriors have had some major changes in appearance.
Even Piccolo couldn't recognize them. Gohan explains that Saiyans have a small appearance for a long time and then suddenly grow tall like weeds after reaching a certain age. In Dragon Ball DAIMA, Goku gave the exact age at which Saiyans start getting taller.
The biggest mystery involving the Saiyans has finally been solved
The reason Goten and Trunks grow up so slowly is because they have not yet reached the Saiyan growth spurt stage. In Dragon Ball DAIMA, Trunks reveals that he is 9 years old. And the Buu saga mentioned that he is 8 years old. That means the events of DAIMA take place about a year after Kid Buu died.
On Trunks' 9th birthday, Krillin mocks him for not having grown much after all these years.
Goku then revealed an important piece of information that made fans wonder why he had never said this before. According to the monkey guy, Saiyans have a growth spurt around age 15, which is consistent with Goku's growth in the first Dragon Ball.
In Dragon Ball episode 1, fans witnessed 11-year-old Goku go with Bulma and defeat bad guys to collect the 7 Dragon Balls. However, Goku was 15 years old when he destroyed the Red Ribbon Army and then finished off King Piccolo.
He wasn't taller then, but a growth spurt was triggered during the three year period following the King Piccolo arc. Goku traveled and trained alone for the 23rd World Martial Arts Tournament when he was just 18 years old. Even 11 year old Gohan was short (when he fought Cell), but grew much taller over the next 7 years and by the time the Great Saiyaman saga began, he was as tall as Yamcha.
But that all changed in Dragon Ball DAIMA, when King Gomah's wish to the Dragon God turned Goku, Vegeta, and the others into 6-year-old children, while Goten and Trunks became infants.
Fans hope Goten and Trunks appear more in Dragon Ball DAIMA
For years, fans have been waiting for Goten and Trunks to be involved in the series. The only time they have an important role in Dragon Ball Super is when they are called in to protect Android 17's island and animals from poachers, while he participates in the Tournament of Power.
Even in the Super Hero prequel in the manga, Goten and Trunks went through their own Great Saiyaman saga where they dressed up to fight bad guys. Later, Bulma found out about it and grounded them for half a year, making all of their training useless. They even forget how to perform fusion or feel Ki.
And just when DAIMA's plot was getting interesting, the creators turned Goten and Trunks into babies. This is basically telling the audience “Goten and Trunks will also not be involved in this story. Sorry!”. Now, fans turn to Toyotaro, the current creator of the Dragon Ball Super manga series, and hope that he will make a difference for these two guys in future arcs.