I am assuming that these are cupcakes that you speak of and hopefully not 18 cakes.
The red velvet cake nor the cream cheese icing should not cause any toxic problems in the pets. It may however upset their stomachs and intestines and could lead to some vomiting and diarrhea. Again the cake and icing itself is not toxic.
Getting into things or changes in diet or exposure to table foods can often cause GI signs. The irritation from these foods alone may cause diarrhea. In other cases, the foods may cause an overgrowth of the bacteria in the intestinal tract which then release chemical called endotoxins. These will cause irritation and sometimes damage to the lining of the stomach and the intestinal tract. Vomiting and diarrhea is often a result of this. In most cases, withholding food for 12 to 24 hours may help to reduce the episdes of diarrhea. Small amounts of water at a time are ok unless she cannot keep it down. If the diarrhea worsens or there is any blood involved, or if she cannot keep food or water down (begins vomiting), you should seek veterinary care immediately. There are a number of good medications availble in injectable forms that may help with vomiting. Unfortunately, there are no good over the counter medications for diarrhea in pets (dosing with some can easily be toxic), and many can be toxic or fatal. One to one and one half tablespoons (based on a standard medium to large breed (60#) size) of pepto bismol every 6 hours is GENERALLY safe, but not reccomended if problems continue after 24 hours. Do not give this if she is on any prescription or over the counter pain medications.
I hope that this is helpful,