ActiveRecord: querying children

I have a parent with has_many children. The children have a column
'blah'. IF I do the following:


The sql exectued is:

    select * from blah where parent_id = 1 and blah = 42
    select * from blah where parent_id = 1

The first line of sql is what I want. The second appears to be
ActiveRecord loading up all of parent.children. This I don't want b/c
children is huge.

How do I avoid that and use idiomatic ActiveRecord?