Labor's school kids bonus will be axed by a coalition government, with Tony Abbott branding the scheme a "cash splash" totally unrelated to education.

The opposition leader confirmed he'd scrap the cash payments to families if elected prime minister, even though the move is likely to be unpopular with voters.

Mr Abbott has been under pressure from the federal government to come clean about the opposition's plans to scrap the scheme, introduced by Labor in the May budget.

He referred to it on Thursday as the issue discussed in an email exchange among himself, his wife Margie and several of his media team and staff, and which was leaked ahead of his address to the National Press Club in Canberra.

In the email chain, Mr Abbott is warned by adviser Andrew Hirst to drop a reference to the axing of an unidentified program.

"I think it's a really bad idea," Mr Hirst wrote.

But Mr Abbott later told the press club he wouldn't shirk the hard decisions, stating up front that the school kids bonus would go if he was elected.

"We did have a discussion via email about a matter, whether it should be in or out," he said of the exchange with Mr Hirst.

"It was the school kids bonus.

"It's not going to happen under a coalition government because it's a cash splash with borrowed money that has nothing to do with education."

The bonus was designed by Labor to give families on Tax Benefit Part A cash payments of $410 for each child in primary school and $820-a-year for each high school student.

Since its introduction, about 1.2 million families across Australia have received $588 million in bonus payments to spend on school equipment, such as shoes or sports gear.

Mr Abbott said he was confident families would still be better off under a coalition government because it would eliminate wasteful and unnecessary government spending.

"We accept that government can't be like Santa Claus," he said.

He also restated his commitment to a "historic" paid parental leave scheme, which would be more generous than Labor's, because it would be a workplace entitlement and not welfare.

Families Minister Jenny Macklin said the coalition would have to introduce a new tax to pay for the coalition's $4.5 billion scheme.