Hi Donna, there are two ways to find their date of death assuming they died in Clark County. First check out Random Acts of Genealogical Kindness, www.raogk.org, choose Washington, choose Clark County. There appears to be a volunteer there who does death lookups and one who will look up obits.
The other way is to contact Clark County Genealogical Society, www.ccgs-wa.org. They should have the Washington Death Index on microfilm and hopefully access to obituaries. They will charge a fee but it should also be a reasonable one.
Once you get the death dates, you can also contact Washington Secretary State, http://www.secstate.wa.gov/library/ask.aspxhttp://www.secstate.wa.gov/library/ask.aspx for a copy of the obituary. They will search the newspaper archives for 30 minutes at no charge & reply with what they find.
In 1900 Ellen and Clarence were living in Baker Creek, Yamhill Co., OR. Clarence, b. NY, 54 yrs old; Ellen, b. IA, 45; Bert F., 21; Charles E., 18; Ethel V., 10; William Fairchilds, father law, 78. Hopefully the childrens' names will be listed in the obits. Successful Hunting!