Critically-ill children will have to travel ten miles or more to get the emergency care they need.
Crawley Hospital will no longer provide emergency or in-patient services for children from the end of this month, despite vehement opposition.
Patients from the Crawley and Horsham areas will be taken over the border to East Surrey Hospital, Redhill.
Surrey and Sussex Hospital NHS trust, which runs both hospitals, says concentrating specialist children's doctors and nurses at Redhill will improve the quality of care given.
But opponents say it will mean longer and more stressful ambulance journeys and parents and relatives will have further to travel when they are visiting.
Michael Edwards, who was involved in the battle to build a new hospital for Crawley, said: "We are sorry the children's ward is going and emergency services will no longer be provided.
"I just hope that the extra time it will take to get a seriously-ill child to hospital will not be the difference between life and death.
"When children have to stay in hospital, obviously their parents and relatives like to be with them constantly. If they live far away, then getting to and from the hospital is going to be difficult for them.
"We have always said a new hospital is the only proper answer as the population is growing all the time."
Under the changes, Redhill will become the centre for children's emergency and in-patient services, including ear, nose and throat.
Both hospitals will continue to provide outpatient and day case treatment.
Crawley's Jumbo children's ward will change its name to Jumbo children's unit and incorporate day surgery patients.
It will also deal with children needing urgent investigation and treatment referred by their GP to a weekday clinic at the hospital.
Catherine Greenaway, lead clinician for children's services, said: "Clinical improvements and better results for patients will be achieved by concentrating specialist children's doctors and nurses at one hospital.
"The majority of children will continue to receive their care locally because they are seen as outpatients or day cases or at the clinics.
"We understand that some other children will have to travel further but the quality of care they receive will be better and access to 24-hour specialist treatment improved."
Hospital chiefs, day nurses and doctors have been fully involved in planning the changes which are designed to provide a balance between centralising specialist skills and equipment in one place and providing as many services as possible close to people's homes.
Children's services at Crawley from October 31 will be:
Day surgery for children who need routine operations or procedures
Child development centre
Community children's nursing team
Children's nurses who specialise in respiratory disease, diabetes and epilepsy
Extending opening hours for GP referral clinic.
Children's services at East Surrey will be:
All emergency services for children in Redhill, Crawley and Horsham
All inpatient services
Day surgery for routine operations and procedures
Children's outpatient clinics
Child health centre
Children's specialist nurses in respiratory diseases and diabetes
GP referral clinic.
The news has angered campaigners have been fighting for years to keep services at Crawley Hospital.
Their fight included an unsuccessful campaign to build a multi-million pound hospital at Pease Pottage.
It was eventually decided to make East Surrey the main hospital for the region while expanding services at the Crawley site.
People wanting to learn more about the changes can call a special helpline set up at East Surrey Hospital.
Call Margaret Farrall or Jancis Graves during office hours on 01737 768511, ext 6961.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article