How do I Aggregate multiple IEnumerables of T

Question

Given....

Public MasterList as IEnumerable(Of MasterItem)
Public Class MasterItem(Of T) 
    Public SubItems as IEnumerable(Of T)
End Class 

I

Answer 1

Just to provide true VB.NET answers:

' Identical to Per Erik Stendahl's and Oliver Hanappi's C# answers
Dim children1 = MasterList.SelectMany(Function(master) master.SubItems)

' Using VB.NET query syntax
Dim children2 = From master In MasterList, child in master.SubItems Select child

' Using Aggregate, as the question title referred to
Dim children3 = Aggregate master In MasterList Into SelectMany(master.SubItems)

These all compile down to the same IL, except children2 requires the equivalent of Function(master, child) child.