A Research Study Looking at How Safe Somapacitan is and How Well it Works in Children Who Need Help to Grow - REAL 9

Inclusion Criteria: Applicable to children with SGA: * Born small for gestational age (birth length below -2 SDS OR birth weight below -2 SDS OR both) (according to national standards). * Age: \- Male participants: Age equal to or above 11.0 years and below 18.0 years at screening. \- Female participants: Age equal to or above 10.0 years and below 18.0 years at screening. * Open epiphyses; defined as bone age less than (\<) 14 years for females and bone age \< 16 years for males. * For Growth Hormone (GH) treatment naïve participants: Impaired height defined as at least 2.5 standard deviations below the mean height for chronological age and sex at screening according to the standards of Centers for Disease Control and Prevention. Applicable to children with TS: • Diagnosis of TS according to local clinical practice. * Age: \- Female participants: Age equal to or above 10.0 years and below 18.0 years at screening. * Open epiphyses; defined as bone age \< 14 years for females and bone age \< 16 years for males. * For GH treatment naïve participants: Impaired height defined as at least 2.0 standard deviation below the mean height for chronological age and sex at screening according to the standards of Centers for Disease Control and Prevention. * For GH treatment naïve participants: Confirmed diagnosis of TS by 30-cell (or more) lymphocyte chromosomal analysis or confirmation of TS and TS mosaicism using comparative genomic hybridization (CGH)-array. Applicable to children with NS: * Diagnosis of NS according to local clinical practice. * Age: * Male participants: Age equal to or above 11.0 years and below 18.0 years at screening. * Female participants: Age equal to or above 10.0 years and below 18.0 years at screening. * Open epiphyses; defined as bone age \< 14 years for females and bone age \< 16 years for males. * For GH treatment naïve participants: Clinical diagnosis of NS according to van der Burgt score list and genetic test result or confirmed mutation in any of the genes associated with NS before allocation. Applicable to children with ISS: * Age: \- Male participants: Age equal to or above 11.0 years and below 18.0 years at screening. \- Female participants: Age equal to or above 10.0 years and below 18.0 years at screening. * Open epiphyses; defined as bone age \< 14 years for females and bone age \< 16 years for males. * For GH treatment naïve participants: Impaired height defined as at least 2.5 standard deviations below the mean height for chronological age and sex at screening * For GH treatment naïve participants: Normal GH secretion (GH peak above 7 ng/mL) during GH stimulation test performed within 18 months prior to screening. * For GH treatment naïve participants: Bone age not delayed more than 2 years compared to chronological age at screening. Exclusion Criteria: * Children with suspected or confirmed growth hormone deficiency according to local practice. * Children diagnosed with diabetes mellitus or screening values from the central laboratory. * Fasting plasma glucose above or equal to 126 milligrams per deciliter (mg/dL) \[7.0 millimoles per litre (mmol/L)\] or * Glycated hemoglobin (HbA1c) above or equal to 6.5%. * Current inflammatory diseases requiring systemic corticosteroid treatment for longer than 2 consecutive weeks within the last 3 months prior to screening. * Children requiring inhaled glucocorticoid therapy at a dose greater than 400 micrograms per day (µg/day) of inhaled budesonide or equivalent (i.e., 250 µg/day for fluticasone propionate) for longer than 4 consecutive weeks within the last 12 months prior to screening. * History or known presence of malignancy including intracranial tumours. Applicable to children with SGA: • Any known or suspected clinically significant abnormality likely to affect growth or the ability to evaluate growth with height, such as, but not limited to: * Poorly controlled or uncontrolled hormonal deficiencies. * Known chromosomal aneuploidy or significant gene mutations causing medical 'syndromes' with short stature, including but not limited to Laron syndrome, Prader-Willi syndrome, Russell-Silver Syndrome, skeletal dysplasias, abnormal short stature homeobox (SHOX) gene analysis or absence of GH receptors. Applicable to children with TS: • Any known or suspected clinically significant abnormality likely to affect growth or the ability to evaluate growth with height, such as, but not limited to: * Known family history of skeletal dysplasia. * Significant spinal abnormalities including but not limited to scoliosis, kyphosis and spina bifida variants. * Any other disorder that can cause short stature such as, but not limited to nutritional disorders, chronic systemic illness and chronic renal disease. * Mosaicism below 10%. * TS with Y-chromosome mosaicism where gonadectomy has not been performed. * New York Heart Association (NYHA) class II or above or requiring medication for any heart condition. Applicable to children with NS: • Any known or suspected clinically significant abnormality likely to affect growth or the ability to evaluate growth with height, such as, but not limited to: * Known family history of skeletal dysplasia. * Significant spinal abnormalities including but not limited to scoliosis, kyphosis and spina bifida variants. * Any other disorder that can cause short stature such as, but not limited to nutritional disorders, chronic systemic illness and chronic renal disease. * Noonan-related disorders including but not limited to: Noonan syndrome with multiple lentigines (formerly called 'LEOPARD' syndrome), Noonan syndrome with loose anagen hair, cardiofaciocutaneous syndrome (CFC), Costello syndrome, neurofibromatosis type 1 (NF1) and Legius syndrome. Applicable to children with ISS: • Any known or suspected clinically significant abnormality likely to affect growth or the ability to evaluate growth with height, such as, but not limited to: * Known family history of skeletal dysplasia. * Significant spinal abnormalities including but not limited to scoliosis, kyphosis and spina bifida variants. * Any other disorder that can cause short stature such as, but not limited to nutritional disorders, chronic systemic illness and chronic renal disease. * Poorly controlled or uncontrolled hormonal deficiencies. * Known chromosomal aneuploidy or significant gene mutations causing medical 'syndromes' with short stature, including but not limited to Laron syndrome, Prader-Willi syndrome, Russell-Silver Syndrome, skeletal dysplasias, abnormal SHOX gene analysis or absence of GH receptors.