In the above example, the Executor of the child's Will would have had to determine the estate tax, if any, the child's estate owed without regard to the existence of the trust. Then the Trustee of trust would have to use the child's Federal Estate Tax Return as the basis for recomputing the child's estate tax liability as if the trust property had been part of the child's estate.
The Executor of a child's Will would have to determine the estate tax owed, regardless of the trust's existence. The Trustee of the trust would then recalculate the child's estate tax liability as if the trust property had been part of the child's estate.