In an ideal world, I think you should have said that you would think about it and found out exactly what it was he was missing and what had changed. As you well know, I have my suspicions about what caused all this in the first place and I think a great deal has been hidden from you.
So now, I would try to repair the haste of your decision by making some conditions. In your shoes mine would be to start talking about what really caused all this, what his feelings are towards you as a romantic partner - and why he has changed his mind. Secondly, I would insist on couples counselling, but even that would come with the condition that he is open and honest with you and the counsellor.
If he agrees to all this, then it would be worth trying again. If he doesn't - or you still feel he's hiding something and isn't really invested in your romantic relationship - then I would ask him to go again.
I understand why you don't want to damage the DCs further by any more disruption, so I think separate chats are called for with them both, as they are such different ages.
To your DD, I would be telling her that you haven't decided yet to take him back, but feel that you should see if anything is salvageable. Really listen between the lines with her though - her reaction to all this has always made me think she is troubled with more than a teenager should have to bear and that there is more to this than just the normal teenage "hating Dad" stuff.
To your DS, I would give a similar message, saying you cannot promise to stay together but that you will be getting some help together to see if you can. I think he particularly needs his expectations to be managed and to understand that it might not all work out in the end after all.
Have you had any individual counselling SD to analyse what you want? I understand that his request was what you were hoping for for so long, but now it's come, are you sure you still want him - and why that is?