Anyone who runs even the slightest fever. This is not allergies. You never run a fever with allergies. So he aparently is running a fever from a slight cold. Also when children have coughing coming and going it also can be a sign of asthma. Especially if he coughs more at night. I suggest you buy even if its allergies. The vicks or cvs brand cool mist humidifier. You fill the tub with water and add a tablespoon of table salt. Place in room at night ,close door 3/4 the way. The only maintenance is to change the filters on top of humidifer evey 3 months. The vicks pediatric size is good even for adults. The vicks one sells for $40 and a 3 pack of filters runs $10. The cvs brand sells for $22. Both can be purchased in local drugstores or on amazon.com. Also where he sleeps at night place a plastic bag on the rug on the floor at night. Take all furry animals out of room. If the cough persist consider seeing a pulmonary doctor to rule out the start of asthma. Singulair is also a great medicine to be on for allergic type symptoms.Either way he should see the pediatrician today.