I promised to treat my kids but now have a problem?

I promised to take my kids to cinema or ice skating today but my 8 year old son has been very rude and abusive towards me. I have given him many chances to redeem his behaviour but he has not changed. I dont feel that he deserves to get treated but the problem is my 5 year old daughter. She has been good as gold and getting very upset about not being able to go out. I am a single mother and have tried hard to get a child minder for my son with no luck. Should I take my son along with us just to not let my daughter down ? I feel so guilty in having to let her down just because of my sons behaviour,