Our kitten was poisoned

We used to have a beautiful orange and brown striped kitten (he was adopted to another home when he was around 9 months).  We have another cat who goes outside on a regular basis and got fleas which she then passed on to Jack (the kitten).  I treated the older cat with Frontline and was going to used a flea and nit comb on the kitten.  My daughter, however, found a very old container of Hertz flea and tick remover and put it on the kitten without telling me.  When we woke up the next morning, poor Jack was shaking violently and had trouble keeping his eyes opened.  I noticed an oily residue on him so I asked my daughter if she knew what it was and she told me about the Hertz.  Knowing that it can be fatal, I rushed Jack to the vet, where he had to stay overnight, got antiseizure meds and fluids, and was thankfully ok after the vet took care of him.  Of course, it cost $400, but it what else could I do?  It was horrible to watch this poor little kitten shaking so violently!