A&E services at County Hospital in Stafford have been suspended for under-18s because "senior clinicians have advised that the service is not currently clinically safe".
University Hospitals of North Midlands NHS Trust brought the interim measure into place from 10am on Thursday, owing to a lack of "professionally trained and experienced staff".
The temporary changes are not impacting the adult A&E, which remains unaffected and open.
Liz Rix, chief nurse and acting deputy chief executive, said: "I fully appreciate the impact these temporary changes will have on families in Stafford and the surrounding area, and understand that people will be very concerned about this news.
"However, we cannot and will not continue to deliver services without the confidence that those services are safe.
"I want to thank my fellow clinical colleagues for reviewing the situation and for their advice, which has led to us taking this difficult short-term decision.
"This allows us the space to examine future options for safe children's services at County Hospital with input from our staff, regulators and partners."
The trust said a clinical model implemented as part of the Mid Staffordshire NHS Foundation Trust Special Administrator recommendations has been deemed "unviable" following a number of safety concerns highlighted in a draft report by the West Midlands Quality Review Service.
These concerns relate to the "lack of sufficient numbers of staff with very specific levels of paediatric and anaesthetic training, including resuscitation and life-support competencies".
Senior clinicians have spoken to staff in detail around the issues highlighted and found the concerns raised by the report "cannot be addressed in the short term", and have led to the temporary suspension of the children's A&E service, said the trust.
Dr Ann Marie Morris, clinical director and emergency medicine consultant, said: "I want to reassure parents that we have taken this decision in the best interests of children.
"Whilst it is regrettable that some children may have to travel further for care, our first priority has to be providing a safe clinical service.
"People view the Children's Emergency Centre as a safety net, but this is only the case when the right number of professionally trained, experienced staff are in place at all times.
"This is not currently the case, and as we cannot resolve this in the short term, the only responsible course of action we can take is to suspend the service."