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Hi, this is Dr. Gabby. It sounds like they had an adverse reaction to the vaccines.
I would give them 1/4 of a human pepcid ac tablet to help settle their stomachs. The pepcid comes in 10 mg tablets and you want to give 1/4 of a tablet every 12 hours until they are eating. You can pop it down their throats and put a few drops of water in their mouths so they swallow. Or crush the 1/4 tablet, mix with water, and give it with a syringe or eye dropper.
To help keep the blood sugar up, since they are not eating, put a few drops of karo syrup, pancake syrup, or honey in their mouths every few hours until they eat again.
See if they will eat some plain cooked chicken. That is easier to digest than kitten food.
Check their gums. If the gums feel dry or sticky they need hydration. You can give them children's pedialtye drink with a syringe or eye dropper every hour until the gums are moist. About 1/2 a teaspoon per hour.
Let your vet know what happened. They may need to be pretreated with benadryl next time.
If they are not back to normal tomorrow they definitely need to see the vet.
Does that help?
Do you have any additional questions?
You are welcome : )