I'm sorry your H is treating his kids so badly but it seems to be something they do.
When my H left he moved straight in with OW and wouldn't tell our DC where he was living for 3 months. It was only when I sent a solicitor's letter that he eventually told us.
I don't know whether it was his decision to keep it a secret or OW's but the reasoning given was to protect OW from us!!!!!
I was horrified at this as I have never approached OW in any way since the discovery of their affair, let alone go to her home and do anything that she needed protecting from. I am not a violent or abusive person, even when pushed by the despair of my marriage falling apart.
Needless to say the DC were devastated at his attitude and told him so, he eventually apologised.
Since H left he has maintained minimal contact with DC, they are away at Uni, he has built a better relationship with one of them and tells things to this DC and not the other, such as where he's going on holiday. It causes no end of friction between the DC and their Dad.
Move forward 18 months and ex and OW have moved again. He is now witholding his new address from DC. How cruel can this man be? The DC are upset once more but they now have an attitude of 'who gives a f**k what he does'. However, as time has passed they have improved things between them slightly, he still puts OW before the DC though, which I will never understand.
So yes these men are very good at just walking away and leaving a trail of hurt in their wake.