Baby sunburn. Use a small child approved moisturizer probably with aloe and nothing to cause allergy or irritate the skin. No alcohol and no retin-a. Just use the moisturizer and keep the skin clean, all should heal fine...If not see a pediatrician. Be sure not to get anymore sunburns as future damage is being done.
Cool and moisturize. Topical cooling will relieve pain immediately. Refrigerated aloe works best. For highly sensitive areas a topical anesthetic can be used under a physicians direction. Oral antinflammatories such as Ibuprofen can provide relief over the first few days. After cooling apply a rich moisturizer such as aquaphor or biafine.
Cool compresses. Baby's skins are very sensitive and burn easily. Try to prevent sunburns by always using sunscreen and staying in the shade. With a minor burn apply cool compresses, give an oatmeal bath and make sure the baby has plenty of fluids to prevent dehydration. If the burn is blistering or baby has a fever bring to the doctor for evaluation.