Hmmm. I think it's safe. But I'm not an expert. I hope someone else with more knowledge comes along to help you out! Does it say anything on the package about age limits?
You should get purina ONE for kittens if you cant get anything besides purina. I personally use Purina ONE healthy kitten formula, I will switch over to SOLID GOLD when he's all done with purina
The Whisker Lickin things are treats. I would say yes, they're "safe" in a reasonable quantity, but the ingredients leave a lot to be desired.
I have 8 cats, so my thoughts on things are maybe different...but one day I realized that my cats would go NUTS over anything that was crunchy that was not their regular food. So I just get small bags of dry food and pass that out as "treats". I haven't brought anything home that they didn't go bonkers for. They have enjoyed Solid Gold, Raw Instinct, Felidae, Wellness, and a bunch of others. Just a thought.