Hi.. this condition is known as papular urticaria..very common problem in children, lesions occuring over exposed areas like face, arms and legs. First and foremost thing to keep in mind is to keep away your kid from mosquitoes as much as possible. Make him wear clothes covering full arms and legs especially evening times. U can also use some mosquito repellant creams and mosquito net at night time. Apply topical fluticasone cream over the lesions twice daily and apply calamine lotion to areas affected which will give him soothing effect. Ucan also give him oral antihistamine for few days to relieve him from itching. Hope this post is helpful to you..