You can do this :

@{
var pagesToList = Current.GetChildrenAsList.Items.Where(node => node.Name.StartsWith(LettertoLookup)).ToList();
}

Thanks dawoe, but I get a:

Cannot use a lambda expression as an argument to a dynamically 
dispatched operation without first casting it to a delegate or 
expression tree type

error when I use that?

This is what I ended up using, thanks for your help, it got me started! Pete.

DynamicNode n = @Model;
 List<DynamicNode> nl = @Model.Children.Items;
   foreach(dynamic item in nl.Where(x => x.Name.StartsWith(currentLetter))){
     <p>@item.Name</p>
   }

is working on a reply...