The Scottish Government needs to take urgent action to stop the equivalent of a classroom of children a day from falling into poverty.
Think tank IPPR Scotland calculated that without new measures being introduced, 50,000 more youngsters will be affected between 2017-18 and 2023-24.
That is the equivalent of 25 children a day entering into relative poverty, it added.
To help tackle the problem, it called on Scottish ministers to bring forward plans to introduce a new family income supplement.
The Scottish Government has already said this is to be brought in in 2022.
But IPPR Scotland director Russell Gunson said action should be taken sooner, before the next Holyrood election in May 2021.
The call for action comes after the Scottish Government’s own advisers at the Poverty and Inequality Commission urged ministers to introduce the initiative quicker.
Mr Gunson said: “It’s not right that almost a quarter of children in Scotland are locked into poverty. And without action that figure is due to rise dramatically.
“Every day the equivalent of a classroom of children are due to enter poverty over the next few years.
“But we know what to do to reduce child poverty in Scotland. We’ve done it before and we can do it again.”
He added: “Much of the increases in poverty in Scotland come from UK benefit cuts and a UK economy that has failed to maintain, let alone improve living standards.
“But here in Scotland, there’s more we can do. Every day, every week and every month of delay matters.”
He added: “The Scottish Government has promised to introduce an income supplement as part of wider plans to help to reduce child poverty.
“This is a golden opportunity to help tens of thousands of children escape poverty in Scotland.
“But given increasing child poverty rates, we want to see urgent action to make a start earlier than planned.
“We believe the Scottish Government can and should bring forward plans for an income supplement before the end of this parliament, and to consider an interim payment before this.”
He made the plea days after the Poverty and Inequality Commission said the Scottish Government would need to invest “considerably more” on tackling child poverty if it is to meet legally binding targets it has set.
Holyrood has already committed to cutting relative child poverty to less than 10% by 2030-31, while reducing absolute child poverty to below 5%.
But figures showed almost a quarter (23%) of children were living in relative poverty in 2016-17, with this forecast to increase to 27% by 2023-24.
John Dickie, director of the Child Poverty Action Group in Scotland, said: “As each year passes childhoods are slipping away, childhoods undermined by the ill health, educational underachievement and stress that poverty too often brings.
“As this report makes absolutely clear, the time for action is now.”
Citizens Advice Scotland policy officer Eilidh McIvor said: “This is a stark warning that should be taken seriously.
“The levels of poverty in our society are already completely unacceptable and the prospect of it getting worse will horrify people across Scotland.”
A Scottish Government spokeswoman said: “Our first Tackling Child Poverty Delivery Plan, published last year, outlines the actions to be taken between 2018-22 – including working towards the development of a new income supplement.
“We have been doing just that and have involved stakeholders, including IPPR, in that work. A one-year progress report will be given to Parliament in June.”