HI. Celestamin tablet can be give half as the weight of your son is 29 kg. Just confirm on the wrapper whether the tablet available with you can be broken to half. This is important as some products should not be cut into half or chewed. Just confirm this. If it is written on the wrapper not to cut , you may also give a full tablet as the weight of your child is 29 kg and the adult dose is 1 to 2 tablets 3 to 4 times a day. Give him a cup of tea or coffee to reduce the sedative side effect of the medicines. Also give plain water steam inhalations and paracetamol if you have. Consult a Doctor now if possible or tomorrow for sure. Do not self treat the boy .