Singer Sia says she knew she had to adopt the child from the moment she first saw him on television.

In an interview with Vogue Australia, the singer opened up about her decision to adopt two 18-year-old boys last year, reports people.com.

"I am obsessed with reality television and documentaries, and I watched a documentary and saw my son," she said.

She shared that she felt an instant connection to the teenage boy after realising he didn't have his own family.

"I was like: 'What? Like, he doesn't have anybody. Oh my God. I'm going to find him and I'm going to be his mummy.' And so that's what I did," she said.

Sia then tracked down the boy and adopted him and his friend.

Sia first confirmed that she welcomed two sons into her family last year, during an interview in May.

"I actually adopted two sons last year. They were both 18 - they're both 19 years old now. They were ageing out of the foster-care system. Yeah, and I love them," she had said.