@nombrecambio
The trouble is, in an ideal world it's something you'd be open with your children about, have a calm discussion about what depression is, how it feels, why it happens (as much as possible) and what everyone involved can do to make the best of it.
However, where depression is symptomatic enough that a primary school child is aware of it and needs to be told is by definition a far from ideal world.
People in the grip of severe depression are not best placed to have that calm, reassuring, considered conversation, or to meet their child's emotional needs for feeling safe and prioritised. So the articulation of it, definitely to the point of knowing about suicidal ideation or intent, just crystallises what the child would have been experiencing as unease into clear and present danger.
I knew my mum was rarely happy. But to be told she felt miserable all the time, that she couldn't remember ever not wanting to be dead, that she had tried to kill herself not once but several times, including on occasions I was in the house and had never realised a thing... I don't think I ever stopped being afraid after that, until she did in fact kill herself last year (I'm now 34). I know it has shaped me, made me who I am today, and not in a good way.
You feel betrayed and lied to; but you were also protected. Even if it didn't entirely work, and you were aware of the problems without really knowing what they were; your family were trying to protect you, thought it was your right to be protected, and their job to do so. No-one tried to protect me. And that has also made me the person I am today. Someone who doesn't expect, can't expect, even the bare minimum of care within a relationship.