Acidental Onion Ingestion!

We had chicken salad sandwiches for lunch and my three-year old is a dwadler. We usually leave her food out for a few minutes, in case she wants a bit more. Apparently, Ruby decided to help herself to the sandwich and shared it with the kittens. The chicken salad is homemade with chicken, celery, onion, and pepper. The was very little onion in it, because I try to pick out my of the pieces for my daughter's sandwiches. Are they going to get sick/die from this?

Oh no! They'll probably be okay. They would have to have eaten a considerable amount of onion to die from it (like, a whole onion each) they may puke or something though. The main concern with onion/garlic is long term exposure to even small amounts because of the way it affects their bodies. As long as this doesn't happen again, they'll be okay.

Why don't you ring your vet and make sure?

I've just gotten off the phone with the vet. I told them I thought that Ruby had eaten most of the "filling" and simply given the kittens the bread to lick. They said it probably won't be a problem and they would be more concerned if the kittens had eaten the bulk of the filling. Also, the sandwich had Miracle Whip in it, which I didn't realize until they told me, has dried garlic in it. I think they'll be ok, I'll just keep an eye on them for a few days.

I'm sure they'll be okay. Jamie got a bowl of tuna salad with a large onion and mayo one time, and he was fine (but so stuffed he could barely move).

It would take more than one helping of a food containing little bits of onions to cause Heinz body anemia.
This usually takes place after a cat has eaten a food containing onions over a period of time, like a cat that will eat only babyfood, etc.
It doesn't take much, granted, but one small indescetion is usually no cause for worry.