引数studentで他の@State変数を初期化しています。

Xcode: Version 12.4

import SwiftUI

struct ChildView: View {
    @ObservedObject var student: Student   //Student: CoreDataのEntity

    @State var name0: String
    @State var num0: Int

    init(student: Student){
        _name0 = State(initialValue: student.name!)
        _num0 = State(initialValue: student.num)
        _student = ObservedObject(initialValue: student)
   }
   var body: some View {
      ...
   }
}

参考：
https://ja.stackoverflow.com/questions/63943/state付きの変数の値の初期化が無効になる