A southeast Queensland man accused of raping his son and daughter would lock one child in a garage cupboard for hours, a court has been told.
The 60-year-old man pleaded not guilty to 12 charges including three of rape at the start of his trial in the Brisbane District Court on Tuesday.
The man from the Redlands, southeast of Brisbane, is accused of having a sexual relationship with his daughter for about half a decade from the time she was about three years old.
He is also on trial for nine offences against his son including assault, indecent treatment and rape.
The jury will hear testimony from the daughter, now an adult, who said the offences that all occurred in her bedroom would happen about twice a week and mostly while her mother was away, prosecutor Jennifer O'Brien said in her opening.
"He told her it was 'our secret' or 'our special time'. At the start she put up a fight but after a while she didn't," Ms O'Brien told the court.
"She describes the conduct becoming so frequent that it became normal."
Ms O'Brien said the man would assault his daughter if she resisted, sometimes kicking her.
It is alleged that at times when she objected he dragged her to the garage and locked her in a cupboard where he stored his tools, sometimes for "several hours".
Ms O'Brien said if the daughter made a noise while locked up her father would "kick the cupboard ... and threaten to do worse".
The nine charges relating to the man's son include digitally raping the boy when he was about seven and threatening to kill him if he told anyone.
It is alleged the man also struck the boy over the head with a liquor bottle at their home, knocking him unconscious.
Ms O'Brien said the man is accused of punching, beating and choking the boy on a weekly basis, once leaving him with red marks and bruising on his neck.
The trial is expected to hear the man drank heavily around the time the alleged offending occurred.
Ms O'Brien said he is expected to tell the court the criminal actions he's accused of didn't occur.
The trial continues before Judge Julie Dick.
