Leader of West Lothian Council, Lawrence Fitzpatrick welcomed the news. He said: "This is fantastic news for residents within West Lothian.
"The council has pressed for a full reopening of the Children's Ward at St John's Hospital for a very long time, as have many local people, and this will be warmly welcomed by the residents of West Lothian."
NHS Lothian will reinstate the service 24 hours a day, seven days a week, from October, to enhance the care already provided to children in West Lothian.
The details were agreed by NHS Lothian board members at their meeting on Wednesday (August 12).