I am a mother of 3, and I homeschool my kids, so there is no break. Ever. Fortunately, they're finally old enough that I can go sit by myself for periods of time, when I need to. This was much more difficult, when they were very young.
Honestly, I don't think it's possible to "protect" your kids from your suffering. Even when you think you're hiding it, they see it, they know. When one person in the house suffers from PTSD, everyone deals with PTSD.
Education has become my best ally. Instead of trying to hide my symptoms, I try to explain them to my kids. They're going to see me cry. They're going to hear me yell. I've even been known to break a dish or two. I've tried to hide it, I've tried to push it down, but it's just not always possible to control the Monster within. And I truly feel like a monster, when emotion hijacks my brain and wrests control of my reactions.
When I realize I've "lost it", I try to leave the room until I can get myself back under control. When I've calmed down, I always discuss what happened, with my kids. I've explained that PTSD is a disorder in the brain, caused by very traumatic experiences, which the brain has difficulty dealing with. Without going into detail, I've described some of the mental/emotional abuse and neglect I suffered as a child. I haven't told them anything about the many instances of sexual abuse, though I have a feeling my 14 yo son has his suspicions. He's asked me about it once, not really meaning to, he was just curious, and (fighting tears and anxiety) I told him that someday I would tell him, but that I'm not ready yet. He left it at that. In many ways, he has become my greatest support (you can imagine how that tears me up inside), and I have to remind myself that he is only 14, as he is mature, far beyond his years.
If I snap at one of the kids (my daughter, especially, has a way of pushing my buttons), I always go back and apologize and talk to them about it. I try to explain to them that it's not their fault, that I cannot handle stress, and it is my flaw, not theirs. I think that part is crucial. My mother used to dump all of her problems on me, and it always made me feel like it was my fault. It is very important, that they know that none of this is because of them, even if I (mistakenly) take it out on them.
The hardest part about having kids, for me, is watching them reach the ages I was, when awful things happened to me. I see how young and innocent they are, and I see myself in them. I was that young innocent girl. I once had that vitality. I had hopes and dreams. Until my vitality was stolen, my hopes crushed, and my dreams shattered. Now, every day, I stumble across the shards of my broken life, constantly cutting myself on the razor-sharp remnants of the girl who was destroyed, to create the shadow of a woman who has taken her place. I miss that girl, but I know she is gone forever. Just as I know that this Shadow will always grieve for her.