Over 100,000 single parents payment cut

More than 100,000 single parents will be cut off from family payments under new measures before parliament.

They'll no longer receive a fortnightly family tax benefit of around $100 when their youngest child turns 13 under the new scaled-back legislation unveiled on Wednesday.

Department of Social Services officials told a Senate estimates hearing on Thursday they expect 136,000 single parents and 76,000 couples to be affected by the cut, while 1.2 million families will get an extra $10 a fortnight under changes to family tax benefit part-A.

A single parent with two teenage children aged 13-15 will get a payment cut of $54 a fortnight.

Although parents cut off from the family tax benefit part-B will get a new $1000 supplement, it's in fact a lot less than what they would have received, about $2737.

The Australian Greens said raising teenagers could be costly.

"It's when growing teens are raiding the fridge, growing, becoming more invested in hobbies and school supplies can get costly," senator Rachel Siewert told AAP.