Anointing of the sick includes the priest laying hands on the sick person and praying, then anointing the forehead and hands with oil.
A couple of questions come to mind. Did you specifically ask (or better, did your son ask) for anointing of the sick? Or did you simply ask the chaplain to come by and see him/pray with him? Do you know that the person who visited was a priest? Often people have the title “hospital chaplain” but are deacons or laypeople. And how old is your son? This sacrament is for those over the age of reason, so it wouldn’t be given to a young child.
Anointing of the sick can be administered to those under the age of reason. I would agree with you that most often it is not, but it can be validly be done. My pastor does administer the sacrament for those who are in danger of death, even for small children. There is physical healing in the grace of this sacrament.
Canon Law does point out the requirement of age of reason and also give the pastoral option if there is doubt. I’ll list the pertinent canons;
THOSE ON WHOM THE ANOINTING OF THE SICK IS TO BE CONFERRED
Can. 1004 §1. The anointing of the sick can be administered to a member of the faithful who,
having reached the use of reason, begins to be in danger due to sickness or old age.
§2. This sacrament can be repeated if the sick person, having recovered, again becomes gravely ill or if the condition becomes more grave during the same illness.
Can. 1005 This sacrament is to be administered in a case of
doubt whether the sick person has attained the use of reason, is dangerously ill, or is dead.
Can. 1006 This sacrament is to be conferred on the sick who at least implicitly requested it when they were in control of their faculties.
Can. 1007 The anointing of the sick is not to be conferred upon those who persevere obstinately in manifest grave sin.