Impetigo (which I think is what you mean) is quite easy to catch - it needs a break in the skin for the bacteria to enter -- nappy rash is often enough to leave a toddler open to infection. Symptoms: "A small patch of blisters that after a few hours breaks into a red, moist area that oozes or weeps fluid; appears mainly on the face, but also on exposed areas of the arms and legs". Many people carry the bacteria without showing any symptoms. Antibiotics clear it up pretty quickly.