What Causes Scab/sores In The Body?

Im a 34yr old male . 128pds 5'4. no past history. recently i got tattoo work on my arms and now i have sores on my tattoos that look infected with yellow coloring an i have a large yellow scab under my nose as well. my girlfriend also has simular sores on her mouth an on her forhead. hers are crusting. my 3 yr old has sores on her arms that look red .could u please tell me what this possibaly is? thank you.