Back in July, the government lost a Senedd vote on extra spending plans after failing to strike a deal with Welsh Labour.
Plaid and Welsh Labour are currently holding fresh budget negotiations around this year’s supplementary budget and next year’s full budget.
In an interview with Walescast, Welsh Labour Leader Ken Skates said: “It appears they’re looking at using Flying Start money to pay for something they never costed during the election or in their manifesto, the childcare offer, which will benefit a lot of middle class and upper class families.
“But it’s going to be people and children who benefit from Flying Start who will pay the price.
“I would be deeply disappointed if Plaid didn’t commit to the future of Flying Start.”
Asked if any change to Flying Start would rule his party out of supporting the budget, Skates replied: “For us as a party, I think it has to be a red line.
“If Plaid Cymru think they can take the best of Flying Start and apply it in different areas, I’m afraid they’re going to let people down badly.
“So, I’m afraid, if they’re talking about Flying Start, then they’re going to have to do it by themselves, without our consent or support and they won’t be getting a budget approval from us.”
Steffan Evans, head of the Bevan Foundation, said: “The majority of children living in poverty are not in Flying Start areas.
“So, if we want to get a childcare system that helps child development in terms of the education and parents back into work and gets to those children in poverty, you do have to strike a compromise, I think, in terms of how that operates.
“And that might mean going towards something more universal to get to more children, rather than something that’s perfect, but only answers part of the problem.”
Reform’s minister for fairness, families and communities, Cristiana Emsley, said: “Plaid Cymru are raising the prospect of cutting funding for vulnerable children while continuing to spend money on overseas embassies, its Nation of Sanctuary programme and tree planting in Uganda.
“At a time when families across Wales are struggling with the cost of living and children are in need of support, it is clear Plaid have the wrong priorities.”
A Welsh government spokesperson said: “Our offer means that childcare will be more accessible and affordable to all families.
“The current phase of delivery which will provide funded childcare for all two-year-olds is being delivered through the Flying Start model.
“At the same time, the support available to disadvantaged children will be enhanced as a result of our offer.
“We will need to substantially increase the number of providers to ensure that families have childcare options that work for them.
“These are all matters under discussion by the Expert Group on Childcare as we work on rolling out the next phase of this ambitious policy.”