The kittens were treated with a flea product by the vet. One of the three drops on the back of the neck. Not sure what, can't remember. Was a bit shocked that they have fleas...well a flea.
fleas have become resistant to some poisons, so if they've had drops but still have fleas you should try another that has a different ingredient. You should wait 4 weeks before putting any more drops on them though because poison.
Which treatment and when?