I’m sorry this is happening, he is doing this to wind you up for Xmas and it has worked.
My advise it to play this as calmly as you possibly can, as if you react you’re giving him just what he wants
Is he supposed to be bring the dc home today?
If so wait until the allotted time, let that pass and an hour later text
Is everyone safe? Only your an hour late for scheduled return of dc
If he then replies not bring them back blah blah
You simply return his text with
Ok, as long as I know the dc are safe & well cared for. I will seek legal advise on2nd Jan 2020
Then leave it...hard as it maybe & believe me I know the sick feeling. Logically it’s not what he’s expecting or wants. He will try and bait you (he’s an abuser) you just reply to any text with I’ll seek advice on 2nd January until then I can’t answer
If he text for uniform or anything, don’t engage, just text back I will contact my solicitor on 2nd January
He’s playing you with these threats don’t give him a reaction or he’ll do it again and again