In a query, can I refer to a subquery column elsewhere in the query?

Is there a way to refer to a subquery column from elsewhere in a query?

In my case I am generating the MIN and MAX of a column in the child table. For the convenience of the statistics consumers, I would also like to provide a column identifying the difference between the MIN and MAX values.

Here's the proof-of-concept SQL:

-- Check for previous version of table to be generated
-- and delete it if it exists
IF OBJECT_ID('dbo.Parent', 'U') IS NOT NULL
    DROP TABLE dbo.Parent;

CREATE TABLE dbo.Parent (
        ParentID varchar(3) NOT NULL,
        ParentDesc varchar(25) NOT NULL
        );

INSERT INTO dbo.Parent values ('P1', 'Parent Rec 1');
INSERT INTO dbo.Parent values ('P2', 'Parent Rec 2');
INSERT INTO dbo.Parent values ('P3', 'Parent Rec 3');

--Create and populate second table
IF OBJECT_ID('dbo.Child', 'U') IS NOT NULL
    DROP TABLE dbo.Child;

CREATE TABLE dbo.Child (
        ParentID varchar(3) NOT NULL,
        ChildID varchar(3) NOT NULL,
        ChildDesc varchar(25) NOT NULL,
        ChildValue numeric(3,1) NOT NULL
        );

INSERT INTO dbo.Child values ('P1', 'C1', 'Child Rec 1',1.1);
INSERT INTO dbo.Child values ('P2', 'C1', 'Child Rec 2',1.2);
INSERT INTO dbo.Child values ('P2', 'C2', 'Child Rec 3',2.2);
INSERT INTO dbo.Child values ('P3', 'C1', 'Child Rec 4',1.3);
INSERT INTO dbo.Child values ('P3', 'C2', 'Child Rec 5',2.3);
INSERT INTO dbo.Child values ('P3', 'C3', 'Child Rec 6',3.3);

-- Perform query

SELECT P.ParentID,
       (SELECT MIN(ChildValue)
        FROM dbo.Child
        WHERE P.ParentID = dbo.Child.ParentID) as MinChildValue,
       (SELECT MAX(ChildValue)
        FROM dbo.Child
        WHERE P.ParentID = dbo.Child.ParentID) as MaxChildValue,
--
--     The following line is the one that's causing the problem
--
       (MaxChildValue - MinChildValue) as ChildValueDifference
FROM   dbo.Parent P,
       dbo.Child  C
WHERE  P.ParentID = C.ParentID
GROUP BY P.ParentID
;

What I get back is the following error message:

Msg 207, Level 16, State 1, Line 41
Invalid column name 'MaxChildValue'.
Msg 207, Level 16, State 1, Line 41
Invalid column name 'MinChildValue'.