I have an abstract parent class A and child classes B and C. I want to declare an abstract method in A such that the implementation in B and C must have a return type of B or C respectively. Is there a way to do this?

sounds like you want self types

generics, or, override the function and narrow the type

Maybe use the Sealed Class and in A use when() with type ?

how will you change the return type with that

I used generics to accomplish that behaviour

abstract class AbstractParentClass<T> where T : AbstractParentClass<T>  {
    abstract fun yield() : T
}

class ActualB : AbstractParentClass<ActualB>() {
    override fun yield() = ActualB()
}

class ActualC : AbstractParentClass<ActualC>() {
    override fun yield() = ActualC()
}