What Are The Red Spots On My Daughter's Chest, Back, Legs And Arms?

my daughter has red spots (some the size of dimes) with white centers over her chest, back, legs and arms. I noticed this on Friday and by Sunday they have doubled in amount. They are a little itchy and she has no fever. One of the spots had scabed over now from the scratching. Wondering what this could be. We were on vacation and playing at a fresh water beach. Out of the 6 of us that were there she is the only one that has this.