The 25-year-old, who cannot be named, was sentenced in Wollongong Local Court yesterday to a minimum 12 months behind bars for touching the little girl while she was on the toilet.

Jailing the man, Magistrate Doug Dick acknowledged the victim had been particularly vulnerable.

The man, who pleaded guilty to indecent assault, walked in on his niece and her brother while they were having a bath last year, the court heard.

The child got out of the bath to go to the toilet and the offender then asked the child if he could use the toilet.

When he was done, the girl sat back down.

The man then stood in front of the toilet, bent down slightly and molested the victim.

Earlier this year, the victim's father was talking to the child about her day when she revealed she had been playing "doctors and nurses" with her friends.

She told her father that during the game, the children had checked shoulders and elbows and had also sometimes pulled down their pants to check their private parts.

The girl confessed her uncle had taught her the game and then the abuse was reported.

Defence solicitor Anthony Williamson told the court the offence was opportunistic but said his client realised there had been a breach of trust.