I just had the same problem with Parent/Child collections and found that post which has solved my case.
I Only wanted to show the List of parent collection items and didn’t need any of the child data, therefore i used the following and it worked fine:
JsonConvert.SerializeObject(ResultGroups, Formatting.None,
new JsonSerializerSettings()
{
ReferenceLoopHandling = ReferenceLoopHandling.Ignore
});
JSON.NET Error Self referencing loop detected for type
it also referes to the Json.NET codeplex page at:
http://json.codeplex.com/discussions/272371
Documentation: ReferenceLoopHandling setting