The only way to remove a tail is either the Kami way or if the saiyan is an adult sometimes it doesn't grow back. Goten and Trunks were only 7 and 8 so there tails would have grown back so we have to assume Dende ripped them off.
OMG lol... Goten nor Trunks never had a tail, it is stated in a Manga. Gohan who is Half saiyan, had a tail and his was even harder to get rid of than Goku's. Some believe Gohan is the most powerful being in the entire universe of DBZ because of this. Yet he was only 1/2 saiyan. Not even Bra, Vegeta and Bulma's second child had a tail and she was 1/2 saiyan. To make things worse, Pan who is only 1 quarter saiyan managed to get an extreme ammount of power by the age of 14 in GT. Yes, some of the timeline in DBZ/GT is a little screwy.
BTW Bulma can get her ass kicked by Chi Chi one on one. Yet Bulma's ammount of IQ could toast ChiChi's.
Hikibi's right, Gohan just happened to win the genetic role of the dice. That probably means that Gohan is more Saiyan than Goten and Trunks, which is strange since Goten seems to be a miniture version of his father and Gohan's something of a pacifist.
Ok... Back to genetics... Seeing on how gohan was the first half human/half saijan he is the first example of what a mixed breed would be. First of all if we're going to talk species than I have to bring up the fact that 2 different spieces can't mate with one and other.
Gohan shows that when a human and saijan are there that there is a tail. Its not a hereditary trait, its a genetic composition. Everything past this is make believe and all myth and dbz geekdom. Gohan was born first with an untapped hidden power. He only touched on this hidden power during the time of the series. If you look at the time goten and trunks were born in relation to their fathers you can see that they had already obtained ssj. So they might be better at handling ssj hereditarily as you see when goten goes ssj on accident. Your going to have to assume that all half saijan/half human children had their tales ripped off at an early age because everyone knew what they could do. Call it a saijan circumsition. I think that covers everything...