You are in a tough spot. If you give in, you may give the impression that will give in and this type of thing will happen more in the future. On the other hand, if you don't give in, you may upset your kids.
Personally, I am inclined to say that you don't give in. It will show your W that she has to honour the arrangements made and that you won't jump at her command. I also think your kids may be initially upset but they will get over it.
I feel for you regarding your anniversary. My first anniversary after Sep was tough.
M35 W37 S9 D6 M12 yrs Know 15 yrs Bomb 1/28/07 My Sitch Failure is the opportunity to start again more intelligently - Henry Ford