SSJ for Goten and Trunks is ok imo... they have pretty much perfect conditions... Saiyan/Human Hybrids are said to generally have more potential: Look where Gohan is when he is a Teenager (SSJ2 = a few billion PL) and then look where Goku and Vegeta were as Teenager (Goku at PL 300 or something like that, Vegeta maybe a few thousand). Gohan simply didn't keep the path of a Warrior and we don't know about Goten/Trunks as GT isnt canon and DBZ ends before they are Adults.
Moreover they can train with some of the best Fighters in the universe... Vegeta, Gohan, Piccolo. AND as motiviation they have this rivalry between them (although they are friends).
Of course it would have been cooler without kids... every SSJ would have his story:
Goku while fighting a seemingly undefeatable villian who starts to kill his friends in front of him.
Vegeta near death and full of anger that he is not "the" legendary SSJ.
Future Trunks because his best Friend and nearly all of Mankind got killed by the Androids.
Future Gohan because Piccolo and Krillin got killed by the Androids.