Parse xml in TSQL: how to loop throw child nodes?

I'm developing a stored procedure for SQL Server 2012 express and developer edition with latest service pack.

I want to parse an XML and insert its data into a table.

This is my XML:

<Parent ParentId="1" ParentCodeId="ASDAS121" ParentLevelId="1">
    <Child ParentId="1" ChildCode="GF342" ChildLevel="0" Position="1"/>
    <Child ParentId="1" ChildCode="G1A42" ChildLevel="0" Position="2"/>
    <Child ParentId="1" ChildCode="GFS42" ChildLevel="0" Position="3"/>
    <Child ParentId="1" ChildCode="GF242" ChildLevel="0" Position="4"/>
                        <!-- N childs more -->
    <Child ParentId="1" ChildCode="DF342" ChildLevel="0" Position="N"/>
</Parent>

This is my stored procedure code:

CREATE PROCEDURE [dbo].[InsertXML]
    @xmlString NVARCHAR(MAX)
AS
BEGIN
    DECLARE @xml xml

    set nocount on

    -- Convert string data into XML.
    SET @xml = @XmlString

    DECLARE @hDoc int

    --Prepare input values as an XML document
    exec sp_xml_preparedocument @hDoc OUTPUT, @xmlData

    INSERT INTO [dbo].[AGGREGATIONS]
        SELECT ID_AGGREGATION, CODE, CODE_LEVEL
          FROM OPENXML(@hdoc, '/Parent', 1) WITH (ID_AGGREGATION bigint '@ParentId', CODE nvarchar(20) '@ParentCodeId', CODE_LEVEL tinyint '@ParentLevelId')

-- I don't know how to continue

    INSERT INTO [dbo].[AGGREGATION_CHILDS]
        SELECT ID_AGGREGATION, CODE, CODE_LEVEL
          FROM OPENXML(@hdoc, '/Parent/Child', 1) WITH (ID_AGGREGATION bigint 'ParentId', CODE nvarchar(20) '@ChildCodeId', CODE_LEVEL tinyint '@ChildLevelId', POSITION int  '@Position')

How can I loop through all children? I don't know how many children will be.