He sent his children to -their aunt's- house. (Special)
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Where did he send his children?

Whose children did he send to their aunt's house?

Who sent his children to their aunt's house?

Who did he send to the aunt's house?

Whose house did he send his children to?

Whose aunt's house did he send his children to?

For more information:

When did he send his children to their aunt's house?

Why did he send his children to their aunt's house?