Welcome and thanks for asking your question. My name is***** am a licensed veterinarian. I am currently not set up to make a live call. But, I am happy to answer your question on this thread.
Friend, the poppy seeds are not going to be toxic. But, the other ingredients in the cake (flour, sugar, oil, etc.) can cause them to develop things like: Vomiting, diarrhea, pancreatitis, etc. I would recommend you keep an eye on them for the next 24 hours. If they develop vomiting or diarrhea this is what you can do:
1- Do not give things like Pepto Bismol or imodium. Start them on Pepcid AC (famotidine) 10mg tablet every 12 hours for the next 2-3 days. You can buy Pepcid AC over the counter in any pharmacy.
2- No food or water for 8-12 hours. Need to give their gastrointestinal tract time to rest.
3- After 8-12 hours offer a small amount of water. Wait half hour, if no vomiting, offer small amount of rice (50%) and boiled boneless chicken or ground beef (50%) 4-6 times a day. Keep on this diet for several days then wean into regular diet.
4- If they continue to vomit after doing the above they will need to be seen by your family veterinarian for a hands on examination.
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