As a child of divorce and having friends who came out of divorce situations so much is variable as to how the parents handle the situation and how involved they staty. BUT kids are very resiliant - and they will do fine. Here are my suggestions based on what I lived through and what I've seen (I'm 51)
1 - Kids have figured out more about the situation that you think. You may assume that they know nothing - but trust me - they have a clue. They've heard conversations in hushed tones, quiet fighting when you thought they were asleep, etc. Have a talk with your kids - keep it bery brief and on a need-to-know basis only. Tell them something like, "all people have problems in some part of their life, your dad and I have our own issues and there's been some painful things that have happened. We're going to see how things go. While there's a chance that we might get back together there's a chance that we won't. But the bottom line is tha we both love you all tremendously and we are going to try our hardest to make sure that we put you first in any decisions that we need to make."
2 - Remind your kids that they are loved and that the break up has NOTHING to do with them. Kids need to be reminded constantly of things - being told something once doesn't do it. So when you think they need to hear it say something like "you know, adults make mistakes, but there's never been anything about you that was ever a mistake - I love you dearly". I remember asking my mom if she could go back in time would she choose not to marry my father (an alcoholic and when he cleaned up at AA became a philanderer who left us for another woman) her answer showed so much love - she said "no becuase then I wouldn't have had my children - if I had married someone else you wouldn't be who you are - and I love YOU."
3 - Involved parents make for stability with kids. Kids need security and they need boundaries. They need to know someone loves them and requires that they stay inside "the circle of protection". We've told our kids since they were little that when they disobey we can't protect them - which is why we set boundaries and limits. As long as dad is still involved and mom is still involved you can both keep the "city walls" up and safe - they know that both parents are going to continue to help them stay safe.
4 - Never ever tell them when they're being rebellious or spiteful (not sure if they're teens - but it's coming - watch for it...) that they can just go and live with their dad. The message they hear is "I only love you when you're easy to get along with - when you're difficult I don't love you". Of course, that's not what you're saying - but that's what they hear. They need to know that there's unconditional love - even in their miserable teenage moments. My child's friend is going through stuff like this now - when the mom says stuff in frustration that's just devastating to him. Teenagers are so tender - even when they seem to be so hard on the outside.
5 - Never let the kids get in the middle -e ven when you can't stand the thought ofhaving to talk to your ex one more time about holiday arrangements, etc - you make the call - don't have your kdis be the messenger.
Finally - just love them, show some grace when they do boneheaded things. Don't tell them that they got that personality trait "from their father" - even when you really really want to! Pray that God's grace covers your mistakes pray for discernment on how to handle difficult situations. I truly believe that God cares about the tiny details of our lives and that if we're following him that all things do work together for good in the end. We go through tough stuff in our life so that one day our expereiences can help others - and make us the people we become. Your kids will come through this beautifully - they will be closer to eachother and closer to you. Expect that they will even show "protective" instincts towards you. Let them. Just keep telling them how proud you are of them. You'll do fine mama - and always give yourself some slack - you are probably handling it all better than you realize!