Returning a row from a function with an appended array field

I have an adjacency list kind of table

CREATE TABLE thingy (
    id int,
    parent int
);

I'd like to be able to write a procedural function that returns a row or
rows from this table with an appended field that represents the children.

Something like this pseudo code:

FOR row IN SELECT * FROM thingy
LOOP
  RETURN NEXT row,[SELECT id FROM thingy WHERE parent_id = id]
END LOOP,
RETURN

Any help much appreciated,

Wes