You said your wife has not started to initiate divorce yet, but said she is going to marry an American. That doesn't sound right logically, unless you two are discuss and try to reach an agreement. If it is the latter case, then you both are talking. That presents an opportunity of indirectly letting her know your plan like"I need to take kids for a vocation so they can enjoy the time with me alone before having to live with your new hu*****and".
On the legal side, you have all rights to take whereever you want. You wife may get upset, but she has no right to prevent your time with your children as long as your action does not put your kids on the harm's way. Otherwise she can make a claim in court to preclude you from custody of your kids.
It's all right for ladies to have their choice of marrying whoever. But our Chinese men always are underdog. That bothers me!