docs: 更新getChildrenData方法文档，修正返回值类型并添加使用注意事项 (#7123)

Author: yvonneyx

packages/site/docs/api/data.en.md

@@ -327,7 +327,7 @@ const comboParent = graph.getParentData('node1', 'combo');
 Get the data of child elements of a node or combo.
 
 ```typescript
-getChildrenData(id: ID): NodeLikeData[];
+getChildrenData(id: ID): (NodeData \| ComboData)[];
 ```
 
 **Parameters**:
@@ -338,9 +338,14 @@ getChildrenData(id: ID): NodeLikeData[];
 
 **Return Value**:
 
-- **Type**: NodeData \| ComboData[]
+- **Type**: (NodeData \| ComboData)[]
 - **Description**: Returns an array of child element data
 
+**Note**:
+
+- **Querying combo's child elements**: If the id corresponds to a combo element, you can directly use this API to get all its child elements.
+- **Querying node's child elements**: If the id corresponds to a node, only when the graph data is a tree structure (i.e., the node data maintains a `children` field, and `children` is an array of child node IDs for that node), can you use this API to get the child elements of that node. Otherwise, an empty array is returned.
+
 **Example**:
 
 ```typescript

packages/site/docs/api/data.zh.md

@@ -327,7 +327,7 @@ const comboParent = graph.getParentData('node1', 'combo');
 获取节点或组合的子元素数据。
 
 ```typescript
-getChildrenData(id: ID): NodeLikeData[];
+getChildrenData(id: ID):(NodeData \| ComboData)[];
 ```
 
 **参数**:
@@ -338,9 +338,14 @@ getChildrenData(id: ID): NodeLikeData[];
 
 **返回值**:
 
-- **类型**: NodeData \| ComboData[]
+- **类型**: (NodeData \| ComboData)[]
 - **描述**: 返回子元素数据数组
 
+**注意**:
+
+- **查询 combo 的子元素**：如果 id 对应的是 combo 元素，可以直接通过此 API 获取其所有子元素。
+- **查询节点的子元素**：如果 id 对应的是节点，只有当图数据为树结构（即节点数据中维护有 `children` 字段，且 `children` 为该节点的子节点 ID 数组）时，才能通过此 API 获取到该节点的子元素。否则返回空数组。
+
 **示例**:
 
 ```typescript