Up to 10 pilot areas were set to start testing new approaches to mental health assessments for looked-after children by May. But a DfE spokeswoman has confirmed that the pilots, first announced in November 2016, have been placed on hold.
The DfE has attributed the situation to the snap general election and the forthcoming purdah period, whereby government departments must not undertake any activity that could call into question their political impartiality, but has declined to comment further.
Under the plans, mental health assessments will be conducted in addition to existing health assessments children receive when they are taken into care.
In January, children's minister Edward Timpson said the Department of Health and NHS England were working alongside an expert working group tasked with developing care pathways for looked-after children with mental health difficulties to develop the scope of the pilots.
In response to a written parliamentary question, Timpson said those working on the project were yet to decide whether the trials would cover care leavers as well as children already in care.
"The terms of reference of the expert working group to develop mental health care pathways for looked-after children explicitly include care leavers," he said.
Mental health charity YoungMinds chief policy adviser Marc Bush urged the government not to delay the trials, as this would "result in thousands of children being placed into care without all of the support they need".
"Children going into care will most likely have faced difficult experiences in their lives which are likely to impact their wellbeing and mental health in the future," Bush said.
"It's crucial that looked-after children are offered mental health assessments so that any support they need is identified and provided to prevent serious and complex mental health problems arising later in life.
"We urge the government to push forward with these trials as soon as possible."
His concern was echoed by policy and research manager at children-in-care and care leavers charity Become, Chloe Cockett, who said the decision could cause "irreversible damage" to children.
"Young people entering care deserve the highest quality support, and this means having proper and appropriate mental health assessments," she said.
"These pilots were vital because all children entering care will have experienced some trauma, and this needs to be identified early to make sure the impact of it doesn't intensify over time.
"This decision to delay the piloting of mental health assessments for this potentially vulnerable group, however impossible it may have been to avoid, may cause irreversible damage to some whose lives have already been turned upside down."
The government announced that it would proceed with trials little more than two months after it rejected a recommendation by the education select committee to ensure all looked-after children are assessed by a mental health specialist when they enter care.
In September 2016, the government had said there was "little evidence to support the claim that a full mental health assessment on or around the time of entry to care for all looked-after children leads to improved health outcomes".