She must tell.  This is one of those places where an adoptive family is different from a bio family.  Our children must be able to trust their adoptive families to be completely open and honest about family background.

Adopted children were not born into happy families.  Their histories normally contain an element of pain and sadness - sometimes severe - that the children must learn to face and accept.  It is the job of the adoptive parent to guide them through difficult elements of their background in an age appropriate way, but it is not our job to mitigate, reinterpret, or otherwise protect them from painful aspects of their families' past.

Personally I would be as matter-of-fact about this as possible.  "My brother decided he didn't want to live any more" is factual and to the point; the child can guide the questions from there.  I generally find that kids ask as much as they want to know, then stop when they've reached their limit.

and my mother who was also bi polar attempted suicide when I was a small child. I truly married my mother and that is no co-incidence. I have a 18 year old daughter and we both found him dead .He was in treatment, on 8 meds and nothing was working. In the end I  concur with my therapist ( who also saw him years ago)that it wasn't the bi polar that killed him, but his relationship with his mother that killed him. Specifically his inability to separate from her. I came from a similar family system and while I am not bi polar and not my husband I too have some of the same  co-dependent/emeshment issues as him .I have been writing about some of this if anyone is interested.see below

http://the-authentic-me.blogspot.com/

Lots written about the disease, but not a lot written about family issues and bi-polar disorder. For me like my daughter the issue is not the suicide, but what its like for a child to grow up with a seriously depressed parent. When I  took my daughter to therapy with me..what emerged was how she often felt like a grown up with him, and how because of his fragility she could never get mad at him.Me I had to keep small and stay out of the way.When my mother went into a mental hospital, I was never told why. And I never asked. But I always told me daughter about her Dads illness, and give it a name when she was old enough to understand.

but I think she needs to be honest.  My DD's biological father "attempts" suicide at least twice a year.  I didn't find out about this habit until she was 8 yo (she's 11 now, he isn't exactly the most involved parent in the world.) It was difficult to talk about it with her, but I'm really glad I did.  The fact that I didn't hide that from her reinforced the trust she already had in me.  Mental illness is an illness as the writer states, so she has not lied to her kids yet, but they may resent her later on in life for hiding it.

My son is also ours through adoption, so I work very hard to be honest about everything, even the difficult and painful. He sees the news or hears the radio sometimes about a murder/suicide and has sometimes joked about killing himself. (usually in fun but sometimes in frustration - he is dramatic and passionate.) I have a cousin who committed suicide and left two children, years ago but I tell him that usually the person's brain is confused and thinks that nothing will be better ever, but that it leaves behind a lot of angry and sad family. I just always try my best to let him know he can ask me anything and I will answer - even explaining some rubbish and foul words he hears at school, just so he knows what something means and that it is not okay. I am fierce in protecting him from bullies, and try to guide him to feel compassion for others.

Hiding family secrets is the worst. Then you can have the kids of someone who committed suicide, and they think they are alone with their problem. Knowing a family history - a true one - is a gift and I wish that I could tell you how much I wish I had one for my China-born son.

As I've shared a number of times here on MT, my brother died of suicide about 13 years ago. Someday I'll have to face this problem myself, how to tell my son. Even though I am a therapist, there is no way I would try this without talking to a therapist myself a few times about this specific dilemma. Why? To explore how, when, and why to talk about my brother's death, without the distortions I bring to it having experienced the death myself.

A couple things cross my mind:

I disagree - professionally and personally -  with the perspective posted above that suicide can be presented as a decision. It is existentially (quite a massive concept for a kid to grasp, no?), and then again it's not - at least not without major caveats. One caveat is that people with major mental illness, of which severe depression is one, are experiencing cognitive distortions that skew the meaning of "decision." Another is that oftentimes alcohol and drug abuse are involved, also skewing the meaning of decision.

There's the story of the death, and the story of the person, which to my mind are not totally the same. One of my challenges will be to help my son know who my brother was - to have a general sense of his uncle - and not to cloud who he was based on how he died. This is one of the burdens of suicide, it's very difficult to bring balance to our memories of the person.

And certainly we have to talk about depression as part of our family history.

My grandfather killed himself long before I was born when my dad was a kid.  Growing up, I knew he had died, but I always was told it was from illness.  When I was around 12, I found out the truth, but felt like I had been majorly deceived the whole time.

It was still pretty much considered a family secret and something that wasn't really discussed.  Then, last year, it was printed in the New York Times in a real estate story about my father's old house, and my mother-in-law sent me an email asking if there was any relation.  I guess the secret's out.

So I think kids should be told when it comes up.  I'm not sure the best age appropriate way is, but maybe you can say he died from depression and talk about it like it's a disease.  I haven't thought this through yet, but considering family history, I guess I should before my kids ask questions.

but in saying yes, I do acknowledge that this is a hell of a journey to have to make.

My paternal great-grandfather spent the last decades of his life in a mental instutition (long story, won't explain here). My great-grandmother, her daughters (one my grandmother) and their husbands told all of their children that the man had died long before they were born. In actual fact, he died when my dad was 13 and he found out about it when he was 16 or so because he discovered a pile of Christmas cards that my great-grandfather wrote my great-grandmother every year until six months before his death. Can you imagine the horror he must have felt? Everyone - the grandmother he revered, his parents, his aunt and uncle, lied. He had a grandfather he never got to meet. And, to worsen the matter, his mother was a social worker and his father was a psychiatrist. It's an anger he still has now, and he turns 70 this year.

This is what I heard from countless psychiatrists as I went through innumerable drug regimens and 4 rounds of shock "treatment". It didn't do me much good to have my feelings of helplessness confirmed by the so-called experts. That said, it is important to take into account the many different kinds of mental illness. For me, it was much more damaging to hear that I had no control than to find out that I did/do. For others, it is important to know that their illness is not something that they may be able to control without intervention of doctors and medication and sometimes those things fail. Point being, I think that stating an absolute either way with regard to choice/control is dangerous. Reality demands complex answers.