Lone parents with children aged 12 or above have already been switched
A welfare reform has come into effect requiring single parents with children aged 10 or 11 to look for work, or risk losing benefits.
Under the new rules, lone parents in this category will be switched from Income Support to the tougher Jobseeker's Allowance.
While this pays the same amount of benefit, parents must show they have applied for jobs in order to claim it.
Last year, single parents with older children faced the same switch.
Work and Pensions Secretary Yvette Cooper said she would make it easier to find work that fits school times.
She said she would do this through new regulations, and changes to how Jobcentres operate.
The move affects 68,000 lone parents.
Single parents of children aged between seven and 10 will be moved to Jobseeker's Allowance in October next year.
The Department for Work and Pensions said the continuing changes are being matched by more "personalised help and support" from Jobcentres, whose staff are being given greater flexibility to respond to a person's individual circumstances.
"Already 80% of all lone parents are either working or would like to work," said Ms Cooper.
"And we know it's much better for families if parents can work. That's why we are changing the rules for parents with older children in school to help them find work."
She added that the government realised that many parents also wanted to work part-time, so they can pick their children up from school.
"We're making it easier for parents to look for jobs that fit with school hours - both through regulations and developing changes to Jobcentres."
The welfare change comes after Ms Cooper said in an interview with a Sunday paper that she wanted employers to offer more part-time jobs for working parents.