Trunks was shown to be stronger than Vegita and in a way stronger than Goku seeing as he took out Frieza and King Cold by himself in a matter of minutes but I usually attribute that to being from the future. Then Goten and Trunks both showed the ability to become Super Saiyan at a very young age and after a week had mastered not only the fusion dance but had reached a level of mastery over their Super Saiyan powers that they could achieve Super Saiyan 3.