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Parent Agent receives no response when Child Agent cannot answer

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Posted on by KT-08120349-0

Hello Community,

I am experiencing an issue with a Parent Agent and Child Agent setup in Microsoft Copilot Studio.

Configuration

Parent Agent uses Agent as a Tool to call a Child Agent.

Child Agent has Knowledge Sources and Generative AI enabled.

Fallback Topics have been configured.

Behavior

When asking the Child Agent directly:

User

↓

Child Agent

↓

No Knowledge Match

↓

Generative AI

↓

Answer Returned ✅

The Child Agent responds normally.

When asking the same question through the Parent Agent:

User

↓

Parent Agent

↓

Child Agent

↓

No Knowledge Match

↓

No Output Returned

↓

System Topic

↓

No Response ❌

What I Observed

The issue only occurs when the Child Agent is invoked by the Parent Agent.

The configured Fallback Topic is not triggered.

The conversation appears to route to a System Topic and then stops silently.

The user receives no response.

Questions

Is this expected behavior when using Agent as a Tool?

Should the Child Agent return a response to the Parent Agent even when no knowledge match is found?

Why is the configured Fallback Topic not triggered?

Is there a recommended pattern to handle fallback scenarios between Parent and Child Agents?

Any guidance or best practices would be greatly appreciated.

Thank you.

Categories:

Bot extensibility

Autonomous agents

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Valantis 6,720 on at

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Hi @KT-08120349-0,

When a child agent is used as a tool by a parent agent, Microsoft docs confirm: "Child and connected agents respect the Use general knowledge setting of the main agent." This means the parent agent's orchestration setting controls what the child can fall back to.

The silent failure you're seeing when no knowledge match is found happens because the child agent returns nothing to the parent when generative AI can't find an answer, and the parent's generative orchestration interprets an empty response as a completed tool call with no output, which then falls through to a system topic rather than the child's configured fallback.

The fallback topic isn't triggered because fallback in a child agent context is only triggered for the child agent's own session. When invoked as a tool, the child runs in the parent's conversation context and the child's system fallback topic doesn't fire in the same way.

The recommended pattern: add explicit instructions to the child agent to always return a response even when no match is found, something like "If you cannot find an answer in your knowledge sources, respond with: I could not find relevant information on this topic." This gives the parent agent something to work with instead of an empty return, which then lets the parent handle the no-answer case in its own instructions or topics.

Alternatively, structure the parent to handle empty or null responses from the child agent tool call as a specific case and route those to your fallback handling.
Ref: https://learn.microsoft.com/en-us/microsoft-copilot-studio/authoring-add-other-agents

Best regards,

Valantis ✅ If this helped solve your issue, please Accept as Solution so others can find it quickly.

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🏷️ For follow-ups @Valantis.

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11manish 3,323 on at

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This behavior aligns with a limitation of the current Agent as a Tool implementation rather than a configuration issue. If you've verified that:

Knowledge Sources are configured correctly,

Generative AI works when the Child Agent is used directly,

Fallback Topics are correctly configured,

then the lack of a response when invoked by the Parent Agent is likely due to the current orchestration behavior of Copilot Studio.

If this scenario is critical for your solution, consider raising a support ticket with Microsoft, as this may be a product limitation or bug. In the meantime, redesign the Child Agent to always return an explicit output (including "no answer found") and let the Parent Agent handle any fallback or escalation logic. This is currently the most robust pattern for Parent–Child Agent architectures in Copilot Studio.

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