The purpose of this study is to find out if somapacitan is safe and how well somapacitan works in children either born small for gestational age or with Turner syndrome, Noonan syndrome or idiopathic short stature. Somapacitan is a new growth hormone medicine for treatment of low level of growth hormone. The study will last for about 3 years. During the study, the participants will be treated with somapacitan once a week. Somapacitan can be injected anytime during the day. The study doctor or nurse will show how to inject somapacitan, so that the participant knows how to do it at home.