As you can see from JObject Documentation,
ChildrenTokens is a
property. The icons with the wrench displays Properties; The blue icon (possibly a lock) is indicating that the property is protected. This would explain why you cannot access it via Intellisense.
You can find a list of the icons and overlays here for VS2015 here: https://msdn.microsoft.com/en-us/library/y47ychfe(v=vs.140)
Note that the icons vary depending on where you are viewing them.