How to use AcDbField::setFieldCode with children?

[daniel_cadext]

the children don't stick

    static auto postToModelSpace(AcDbEntity* pEnt)
    {
        if (pEnt == nullptr)
            return std::make_tuple(Acad::eNullEntityPointer, AcDbObjectId::kNull);
        AcDbObjectId id;
        AcDbDatabase* pDb = acdbCurDwg();
        AcDbBlockTableRecordPointer model(getblockModelSpaceId(pDb), AcDb::OpenMode::kForWrite);
        Acad::ErrorStatus es = model->appendAcDbEntity(id, pEnt);
        return std::make_tuple(es, id);
    }

    static auto entsel(const TCHAR* msg = L"\nSelect Entity: ", const AcRxClass* desc = AcDbEntity::desc())
        -> std::tuple<Acad::PromptStatus, AcDbObjectId, AcGePoint3d>
    {
        AcDbObjectId id;
        AcGePoint3d pnt;
        ads_name name = { 0L };
        auto res = static_cast<Acad::PromptStatus>(acedEntSel(msg, name, asDblArray(pnt)));
        if (res == Acad::eNormal)
        {
            if (auto es = acdbGetObjectId(id, name); es != eOk)
                return std::make_tuple(Acad::PromptStatus::eError, id, pnt);
            if (!id.objectClass()->isDerivedFrom(desc))
                return std::make_tuple(Acad::PromptStatus::eRejected, id, pnt);
        }
        return std::make_tuple(res, id, pnt);
    }

    static void createField()
    {
        using AcDbFieldPtr = AcDbObjectPointer<AcDbField>;
        using AcDbMTextPtr = AcDbObjectPointer<AcDbMText>;

        auto [ps, id, pnt] = entsel(L"\nPick a line", AcDbLine::desc());
        if (ps != Acad::PromptStatus::eNormal)
            return; //oof

        AcDbDatabase* pDb = acdbCurDwg();

        //child1
        auto childCode1 = std::format(L"%<\\AcObjProp Object(%<\\_ObjId {}>%).Layer>%", id.asOldId());
        auto childFlag1 = AcDbField::FieldCodeFlag(
            AcDbField::FieldCodeFlag::kObjectReference |
            AcDbField::FieldCodeFlag::kPreserveFields
        );
        AcDbFieldPtr childField1;
        childField1.create();
        childField1->postInDatabase(pDb);
        childField1->setEvaluationOption(AcDbField::EvalOption::kAutomatic);
        childField1->setFieldCode(childCode1.c_str(), childFlag1);
        childField1->evaluate(AcDbField::EvalContext::kDemand,pDb);
        acutPrintf(L"\nchildField1 = %ls", childField1->getFieldCode(AcDbField::kEvaluatedText));

        //child2
        auto childCode2 = std::format(L"%<\\AcObjProp Object(%<\\_ObjId {}>%).Length>%", id.asOldId());
        auto childFlag2 = AcDbField::FieldCodeFlag(
            AcDbField::FieldCodeFlag::kObjectReference |
            AcDbField::FieldCodeFlag::kPreserveFields
        );
        AcDbFieldPtr childField2;
        childField2.create();
        childField2->postInDatabase(pDb);
        childField2->setEvaluationOption(AcDbField::EvalOption::kAutomatic);
        childField2->setFieldCode(childCode2.c_str(), childFlag2);
        childField2->evaluate(AcDbField::EvalContext::kDemand, pDb);
        acutPrintf(L"\nchildField2 = %ls", childField2->getFieldCode(AcDbField::kEvaluatedText));

        //parent
        AcDbFieldArray children;
        children.append(childField1);
        children.append(childField2);

        const auto parentCode = L"hi %<\\_FldIdx 0>%, %<\\_FldIdx 1>%";
        auto parentFlag = AcDbField::FieldCodeFlag(
            AcDbField::FieldCodeFlag::kTextField 
        );
        AcDbFieldPtr parentField;
        parentField.create();
        parentField->postInDatabase(pDb);
        parentField->setEvaluationOption(AcDbField::EvalOption::kAutomatic);
        parentField->setFieldCode(parentCode, parentFlag, &children);
        parentField->evaluate(AcDbField::EvalContext::kDemand, pDb);
        acutPrintf(L"\nparentField = %ls", parentField->getFieldCode(AcDbField::kEvaluatedText));

        //set
        AcDbMTextPtr pMtext;
        pMtext.create();
        pMtext->setLocation(pnt);
        postToModelSpace(pMtext);
        AcDbObjectId fid;
        pMtext->setField(L"TEXT", parentField, fid);
    }

    static void AcRxPyApp_idoit1(void)
    {
        createField();
    }

the result:

Command: IDOIT1
Pick a line
childField1 = 0
childField2 = 19.036052
parentField = hi ,