Can children get pulmonary hypertension?

Yes. Sometimes there are congenital cardiac defects that can cause pulmonary hypertension even in newborns. While rare, a pulmonary embolism can cause acquired pah in a child. Primary pah can occur in the teen years. Secondary pH can occur with lung diseases such as cystic fibrosis.
Yes. Children can certainly--and unfortunately--develop pulmonary hypertension. I care for many with the condition.
Yes. There children are at risk of developing this disease. If you are concerned about a child having this disease, you should ask your pediatrician. The sooner this disease is identified the better it is for the patient.