Is it possible for a 12weeks old baby to get ring worms on their skin n what courses it?

Fungal infection: Yes, it is possible. It is caused by a fungus called Tinea. To have a confirmation of this type of skin infection and to get the appropriate treatment you need to have your child's pediatrician have a look at the baby's skin.

First question, yes: Any rash in 12 week old should be seen fairly promptly by the pediatrician or primary doctor. It is very possible for an infant to get ringworm. It is a skin fungus that is usually harmless in healthy older children and adults. Are there any kittens or other new pets in the home? As ringworm is an opportunistic infection, it is important to get correct dx and make sure it isn't serious.