ex refuses to take the kids for a week so i can go on vacation

I have been burnt out lately and finally booked a solo tour to Greece. Found a great deal on Industravel and thought I need it to recharge. I asked my ex-wife to take the kids for that week and offered to take them for two extra weeks when I get back to make up for it. She refused and said she isn't going to babysit her own children just so I can go on a vacation. Now she is saying I am abandoning them, but I think I deserve a break.