My three year old son has a cluster of little blisters on his wrist. They don't feel itchy and don't hurt. I first noticed one blister in the same spot a day or so earlier I thought it was a tiny scrap that was getting infected because it looked like a pimple with a scab on top. So I scraped and cleaned it, and now there are four more blisters in the same area, seems to have spread. What could this be? Should I be very concerned?

Could be Poison ivy or another contact dermatitis. Any in the yard?