Mine did this too, he knew mentally how down i was, not coping at all with him ending our marriage, 3 years after the sudden death of our eldest son, and i got endless emails telling me he'd arranged with our 2 youngest sons specific days and dates when he'd be seeing them, that they both wanted to be with him not with me. That they'd be spending more time with him, then me.
At the time i believed everything he was telling me, i was so determined not to involve our two youngest sons in his arguments with me, i was too scared to say anything to them about it.
Turned out to be all bluff, he was mostly living with his new gf then anyway, spending his time with her 3 kids, rather then ours, but i didn't know it at the time.
Even the week after our middle son was 18, i was still getting emails telling me he was going for custody of him! At the same time this son was found on the verge of suicide, he was in such a state over his Dad's actions, and becoming the same age as his brother was when he died.
Eight months later when i finally received divorced papers, he'd completed the child access one for our youngest son, just putting 'informal access' aranged!
I'd take everyones advice above, learn from their experiences, he's just trying to continue putting you through the worse pain possible, and using your precious children as weapons to do so.
You shouldn't have to go through this, by the father of your children, but the more time i spend on MNs the more i'm realising its happening to everyone whose husband walks out on them, they really do follow 'the script' if you havn't read about it already, do so, its an eyeopener.
Sending hugs, from a mum whose already gone through this, and knows how much panic and worry it causes xxx