There are a number of agencies and nonprofits with resources on suicide and coping with suicide. A number of links are on this page:

http://www.nasponline.org/resources/crisis_safety/suicideprevention.aspx

This page in particular has a list of tips on speaking to younger children, including some books:

http://www.save.org/index.cfm?fuseaction=home.viewPage&page_id=EB8CDAFC-7E90-9BD4-CDB77DB42FD5C2CE

There are lots of resources on mental illness, including depression, aimed at teens, but probably still useful for high-functioning pre-teens, with much accessible technical info (if that isn't an oxymoron!) at

www.copecaredeal.org

including downloadable first-person accounts of living with depression, suicidality, anxiety, eating disorders, schizophrenia, etc.

This is a brief cut sheet of tips for helping suicidal peers (originally developed after 9/11, but obviously of general use):

http://www.nasponline.org/resources/crisis_safety/savefriend_general.aspx

Never be afraid of talking about suicide with children (at their level). It does not "put ideas in their heads," unless those ideas were already there. One does have to be careful about glorifying the victims of suicide, as that is believed to be the main impetus behind the contagion effect. CollinsMum is right; this can be a very good opportunity to communicate to your pre-teens that you will listen without judging to whatever they have to say about their experience.

...pronounced like the long vowel and first letter of the alphabet...