困扰好几个小时的问题终于解决了，本人系菜鸟，使用MVVM设计模式，绑定DataTemplate的Command，需要使用
DataContent的资源,否则无法触发ICommand ClickChildMenu
下面是关键代码：
<TextBlock Text="{Binding Title}" FontSize="12" >
<i:Interaction.Triggers>
<i:EventTrigger EventName="MouseLeftButtonUp" >
<i:InvokeCommandAction
Command="{Binding ElementName=LayoutRoot,
Path=DataContext.ClickChildMenu}"
CommandParameter="{Binding}" />
</i:EventTrigger>
</i:Interaction.Triggers>
</TextBlock>
<toolkit:Accordion x:Name="theList" SelectionMode="ZeroOrOne" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" FontSize="12" ItemsSource="{Binding Catalog}">
<toolkit:Accordion.ItemTemplate>
<DataTemplate>
<StackPanel>
<TextBlock Text="{Binding CatalogName}" FontSize="12" />
</StackPanel>
</DataTemplate>
</toolkit:Accordion.ItemTemplate>
<toolkit:Accordion.ContentTemplate>
<DataTemplate>
<ListBox x:Name="mListBox" ItemsSource="{Binding ChildMenus}" BorderThickness="0" >
<ListBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Title}" FontSize="12" >
<i:Interaction.Triggers>
<i:EventTrigger EventName="MouseLeftButtonUp" >
<i:InvokeCommandAction
Command="{Binding Source={StaticResource vm},
Path=ClickChildMenu}"
CommandParameter="{Binding}" />
</i:EventTrigger>
</i:Interaction.Triggers>
</TextBlock>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
</DataTemplate>
</toolkit:Accordion.ContentTemplate>
</toolkit:Accordion>