The purple hind legs of newborn kittens may be caused by poor blood circulation or frostbite. In this case, it is suggested to seek the help of a veterinarian immediately, because it may be a serious disease or injury, such as frostbite, fracture, arthritis and so on.

While waiting for veterinary treatment, the following measures can be taken to alleviate the symptoms of kittens:

1. Provide a warm environment for kittens, such as using electric blankets or blankets.

2. Gently massage the kitten's hind legs to promote blood circulation. Be careful not to overdo it, so as not to cause more harm.

Provide the kitten with enough food and water to ensure its health.

Please be careful not to give the kitten drugs or other unauthorized treatments. Please follow the veterinarian's advice and guidance when dealing with kittens.