4 year old has got the cold will vapour rub help unblock his nose and help his chest?

Use sparingly: and it might help. Cool humidified air will also help and if he is coughing a warm drink with honey will relieve the cough. For severe nasal congestion it is ok to use a small amount of afrin nasal spray for one or two nights only to unblock the nose. Be sure to not use it more than that as it is not approved for use in children.

I avoid it: I look at any odor producing material like vaporub as a nasal irritant, not a solution to any problem. Adults with mature noses can tolerate the material with less internal swelling than kids. I never use it before school age and use it infrequently for them.