How to include a child object's child object in Entity Framework 5

If you include the library System.Data.Entity you can use an overload of the Include() method which takes a lambda expression instead of a string. You can then Select() over children with Linq expressions rather than string paths.

return DatabaseContext.Applications
     .Include(a => a.Children.Select(c => c.ChildRelationshipType));

With EF Core in .NET Core you can use the keyword ThenInclude :

return DatabaseContext.Applications
 .Include(a => a.Children).ThenInclude(c => c.ChildRelationshipType);

Include childs from childrens collection :

return DatabaseContext.Applications
 .Include(a => a.Childrens).ThenInclude(cs => cs.ChildRelationshipType1)
 .Include(a => a.Childrens).ThenInclude(cs => cs.ChildRelationshipType2);

I ended up doing the following and it works:

return DatabaseContext.Applications
     .Include("Children.ChildRelationshipType");