The abuse began when they were so young and happened so often that the girl thought it was normal.
She now suffers flashbacks and nightmares as a result of what happened.
Heartless Abbott, who has a previous conviction for child neglect, denied she’d done anything wrong, forcing the children to give evidence against her.
But a jury unanimously convicted her of three sexual assault charges and two of assault yesterday and she was placed on the Sex Offenders’ Register.
The children told how they would wake up to find Abbott, of Dalmellington, East Ayrshire, in bed beside them.
The abuse began when Abbott was 28 and was looking after the children, who can’t be identified for legal reasons.
She made the boy watch porn and tried to force him to have sex with her when the boy was aged just five.
Kilmarnock Sheriff Court heard it was not possible because the boy was so young he was physically unable.
She then forced him to take part in sexual activity.
The abuse stopped when he turned seven.
Abbott began abusing the girl when she was six.
The girl told the court she would wake up to find Abbott lying on top of her.
The abuse lasted until she was 11 or 12.
She also beat the children, repeatedly punching and slapping them on the head and body.
Giving evidence, the girl said: “I wasn’t too sure about the sexual abuse and then when I realised what was actually happening I didn’t know how to tell anyone.
“As it started at such a young age I didn’t really understand what it was.
“I thought it was normal at that point in time, but the older I got I started to realised it wasn’t normal.
“I felt ashamed.”
Prosecutor Craig Wainwright said: “She abused her position of trust over the children for her own sexual gratification.
“She also assaulted both children on a number of occasions.
“All the occasions [of sexual abuse] were at night, at a time when she was drinking.”
The court heard it took the children so long to go to police due to shame and embarrassment at what had happened to them.
Mr Wainwright added: “He found it hard to come to terms with being a male who was sexually abused by a female.”
After the verdict, Sheriff David Hall said it was “an anxious case” and continued Abbott’s bail ahead of sentencing.