Keep an eye on the kitty, just to be safe, but I have a cat that tries to eat the green leaves every year they come up. I have never let her eat the petals of the flower, but she oddly never gets sick, but I think she knows her limits too, so keep your eyes open. Hope this helps, good luck to you.
Ingestion of tulip leaves can cause vomiting and possibly diarrhea. When kittens have gastrointestinal upset (vomiting and diarrhea) they can become dehydrated, hypothermic, and hypoglycemic very quickly. If your kitten starts exhibiting signs have him examined by a veterinarian.