The parents defending their babies in this video do so with great effectiveness. Porcupine quills are deadly. There are many cases of leopards and for example lions dying after being harpooned by porcupine quills because they tried to attack the animal.
Once the quills have been inserted into a predator like a leopard they are released from the porcupine and the barbs on the quill means that movement by the leopard forces the quill deeper into their body and they are impossible to extract. They can cause an infection.
A study published on the science.org website tells us that "a porcupine quill needs only about half the force of a hypodermic needle" to pierce skin. Interestingly, they studied porcupine quills to see if they could improve the design of medical instruments!
Porcupine quills are large stiff hairs. The North American porcupine has about 30,000 quills. Each one is adorned with between 700 and 800 barbs along the 4 mm of the tip. The barbs help the quill remain embedded in the victim's skin.
Barbed quills required about half the penetration force of quills that do not have barbs. And, as mentioned, 56% of the force needed for a hypodermic needle to be inserted into human skin.
The barbs mean that they are four times harder to pull out once they are embedded. The barbs located within the 1 mm tip of the quill contributed to about 50% of the pull-out resistance.
Porcupines do not shoot their quills at predators but they detached easily when touched. I have seen many pictures of large wild cats such as pumas with quills in their snouts. When that happens, they can't do a thing in terms of predation. The puma with a face full of quills is going to starve to death. This is why porcupines are very dangerous animals to wild cat predators and which is why the defensive measures put up by the parents and the video are so effective.