Well it could be something very serious. Even very serious to a human. I once had a large lump in my leg with a hole in it and it ended up being a spider bite where I had venom on it but I was too large for it to hurt me very badly. But since it is a baby kitten I would advise you to take it to a vet ASAP because since it is a kitten it is not quite strong enough to fight off something of any nature like that so please get the kitten treated good luck.

 It is an infection and the best place for help is the vet.

 It most likely is an infection. If it oozes white goo when you press it, it definitely is an infection. The best thing to do is to get your cat an appointment and once maybe twice a day squeeze the spot gently to get some of the infection out. (Very disgusting look and sometimes smell though)

 It sound like an open abcess, (Boil) if there is puss weeping from the wound a trip to the vet is warrented, most infectious bacteria can't cross from animals to people, but your other cats could be infected. If there is no fluid, or only clear, a spider bite is likely, again a vet trip is called for.