coroutine parent child relationship

coroutine_parent_child.kt

fun main() = runBlocking<Unit>{
    launch(Dispatchers.Default) {
        repeat(5) {
            println("coroutine 1: $it")
            delay(500)
        }
    }
    launch(Dispatchers.Default) {
        repeat(5) {
            println("coroutine 2: $it")
            delay(500)
        }
    }
    delay(1500)
    coroutineContext[Job]?.cancel()
}

//console output
coroutine 1: 0
coroutine 2: 0
coroutine 1: 1
coroutine 2: 1
coroutine 1: 2
coroutine 2: 2
Exception in thread "main" kotlinx.coroutines.JobCancellationException: Job was cancelled; job=BlockingCoroutine{Cancelled}@61e717c2