Short answer: Prefect doesn’t automatically aggregate subflow logs into the parent flow run. Each subflow is its own flow run with its own log stream. There isn’t a UI toggle to “show child logs in parent.” That said, you can deliberately “double log” from a subflow into the parent’s log stream using

flow_run_logger(parent_flow_run_id)

. Here’s a small pattern you can drop into your subflows:

from prefect import flow
from prefect.logging import get_run_logger, flow_run_logger
from prefect.context import FlowRunContext

def _both_loggers():
    # Returns (child_logger, parent_logger or None, context)
    child_logger = get_run_logger()
    ctx = FlowRunContext.get()
    parent_id = getattr(ctx.flow_run, "parent_flow_run_id", None)
    parent_logger = flow_run_logger(parent_id) if parent_id else None
    return child_logger, parent_logger, ctx

@flow
def child_flow():
    child_log, parent_log, ctx = _both_loggers()

    def log_both(msg, level="info"):
        getattr(child_log, level)(msg)
        if parent_log:
            # add a prefix so parent logs are distinguishable
            getattr(parent_log, level)(f"[subflow {ctx.flow.name} | {ctx.flow_run.id}] {msg}")

    log_both("Child work starting")
    # ... your logic ...
    log_both("Child work finished")

Notes and best practices: - This will emit logs twice (once to the child flow run, once to the parent). Consider forwarding only key events to keep parent logs readable. - Prefix forwarded messages with the subflow name/run ID so parent logs are clear. - If a flow is invoked top-level (no parent),

parent_flow_run_id

is None and forwarding is skipped. Alternative approaches: - Use a correlation ID (passed from parent to subflow) and query/aggregate logs across runs with the API if you prefer not to duplicate logs. - You can fetch all related logs programmatically via

PrefectClient.read_logs

and

LogFilter

and present/ship them elsewhere. Helpful docs: - Subflows and flow runs: Flows (subflows) - Logging how-to guide: How to add logging - Loggers API (includes

flow_run_logger

): prefect.logging.loggers If you want, I can help you wrap this into a small utility so all your subflows automatically forward selected log levels to the parent. Would you like to forward all logs or just INFO+/errors?