(West Linn, OR)  --  Clackamas County health officials say three pre-school children in West Linn have been sickened by E. coli.  The health department says all children at Heart Centered Montessori School will be tested to determine whether anyone else is infected with E. coli but not yet showing symptoms.  Officials say two children were hospitalized in September and October after becoming sick with a potentially deadly strain of E. coli, and a third child tested positive for the bacteria.  The health department says it hasn't found the source of the E. coli.