I personally would have called a week before and asked if the casino night was still on.. and then on the day politely explained that Ds was having a majorly bad day and would it be to much trouble for them to find someone else to go..

I think you both have the right to be annoyed though :/ It is hard to have friends who don't have kids or who have much older children. Friends of ours don't have children and think its easy to go places or catch up at night ect.. They recently applied to be foster parents and had some children recently for afew days.. Their FB status said it all.. We now have a renewed respect for parents with more then 1 child

I don't think they will be rushing to offer too much advice now as I think they have realised it is not as easy as it looks sometimes.. but back to you.. If you don't want to call maybe an email with an apology and say you were really distracted that day with your DS and invite them over for a meal and a movie??