As shown in the classic Dragon Ball Z, Goku, Vegeta and Gohan had to undergo intense training and practice before they were able to become Super Saiyan.
However, this does not seem to apply to Goten and Trunks. Although I could see Trunks also had immense training with his dad Vegeta, he still seemed to take less effort than the other 3 to turn Super Saiyan.
Also, Goten becoming a Super Saiyan doesn't make sense to me. According to the series, Goten was able to turn Super Saiyan just from being trained by Chi-Chi. How is that possible? How could Goten and Trunks (to quote Vegeta) turn SSJ like it's a Super Saiyan bargain sale?