It is recommended to put the children first.
Are they in any immediate physical, mental or emotional danger? If so, take any action needed to get them to safety.
If it is just a mind game your ex is playing with you, don't play.
Is your ex threatening to prevent you from seeing your kids if you don't do this, that or the other? That's only going to work in the short term.
Kids have brains and know how to use them. They grow up and become independent.
If you consistently remain supportive of them, show them how much you love them, and never stoop to the low levels of your ex, your relationship with your kids will remain strong and close.