The little boy also reported that he had been targeted by his father up to 80 times over a five-year period.
Details emerged as the man failed in a legal bid to overturn convictions for molesting his children.
He is serving a 14-year sentence imposed at Dungannon Crown Court in 2017 for sexual assault and multiple counts of rape committed between 2009 and 2014.
The abuse began when the boy was four and ended when he was eight, while his sister was five when she was assaulted.
Aged in his forties and referred to as RD to protect his children’s identities, the man denied the charges and claimed their mother had encouraged them to give false evidence.
His challenge to the convictions centred on the trial judge’s charge to the jury.
The Court of Appeal heard how the children revealed the abuse to their mother in April 2014 following concerns about the boy’s gait when walking.
He told her that his father had been “hurting me”, while his sister stated she walked into the room during one incident and admonished “bad daddy”.
The boy reportedly said the sexual offending happened between 70 and 80 times.
He also alleged that his father threatened to shoot both children if he told anyone.
Ultimately, however, the jury cleared RD of making threats to kill his son and daughter.
Dismissing the appeal against the rape and sexual assault convictions, judges rejected grounds based on directions given to jurors and evidence from the children’s mother.
Lady Chief Justice Dame Siobhan Keegan held that none of the arguments succeeded in a challenge mounted out of time.
She said: “Whilst there were some issues with the charge, the court does not have any sense of unease about the safety of this conviction.”
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