There are several possibilities including bites (fleas or other), eczema
or allergic contact dermatitis
, lichen planus
), and others. I doubt bed bugs
given the location. I would recommend you try a moisturizer such as cerave cream twice daily and if not better after a few days consider a trip to the dermatologist for diagnosis and treatment options. Bites are common in kids so that is certainly a possibility. If they are bites, avoidance plus a steroid gel might be beneficial. I hope that helps.