What's the best way to talk to a twelve year old about suicidal thoughts?

Directly: Often people think that talking about suicide makes it more likely - it is actually the reverse. An important questions is what makes you ask? If you are concerned about your child having suicidal thoughts ask them directly if s/he has ever thought about hurting themselves. Also ask if they think about not living sometimes. What they know and think about suicide. Seek the help of a therapist.