 <p>You need to annotate the collection with <code>DataMember</code> or it will not get serialized at all. You will also need to annotate the <code>DataContract</code> with <code>KnownType(typeof(ChildCollection))</code> as otherwise it doesn't know what type of "thing" the <code>ICollection</code> is and therefore how to serialize it</p> <p>Similarly you will need to add <code>[DataMember]</code> to <code>Child_A</code> <code>Name</code> property or it will not get serialized</p>