Considering code like this.

def child_flow_c():
    d = run_deployment("child-flow-d/dep-child-d")
    # How can I be sure that run_deployment("child-flow-d/dep-child-d") is completed before moving to next line/deployment 
    e = run_deployment("child-flow-d/dep-child-d")

How we check the status of

run_deployment

is completed before executing another

run_deployment

You should be able to add polling and timeouts. But in the API ref it mentions that:

This function will return when the created flow run enters any terminal state or the timeout is reached.

https://docs.prefect.io/latest/api-ref/prefect/deployments/#prefect.deployments.run_deployment

Thank you I will try that out.