Goten never had a tail either from what i've seen. It was always my understanding that when saiyans are kids they have a tail that grows back if its cut off. Adults can have a tail, but if it gets cut off it does not grow back again. I don't know why trunks or goten never have a tail, maybe they did but their mothers (chi-chi and bulma) keep them cut off for reasons of safety.
RogueMartian, Prisoner of Circumstance
I'm gonna sleep this off like a baaad hangover
"Cuz, y'know, nothing says stealth like neon-friggin'-orange." -Conekiller