A Research Study to See How Much CagriSema Lowers Blood Sugar and Body Weight Compared to Placebo in Children and Adolescents With Type 2 Diabetes

Key Inclusion Criteria: * Informed consent of parent(s) or legally acceptable representative (LAR) of participant and child assent, as age-appropriate, obtained before any study-related activities. Study-related activities are any procedures that are carried out as part of the study, including activities to determine suitability for the study. * The parent(s) or LAR of the child must sign and date the Informed Consent Form (according to local requirements) * The child must sign and date the Child Assent Form or provide oral assent (according to local requirements) * Male or female. * Age 10 to \< 18 years at the time of signing the informed consent. * Diagnosed with T2D (according to the latest International Society for Pediatric and Adolescent Diabetes \[ISPAD\] criteria) ≥ 30 days before screening. * Treated with diet and exercise counselling alone or with a stable daily dose(a), in addition to diet and exercise counselling, of any of the following antidiabetic drugs or combination regimens: * Insulin (any regimen) * Metformin * SGLT2i * HbA1c 6.5%-11.0% (48 mmol/mol - 97 mmol/mol) (both inclusive) as determined by central laboratory at screening. * Body weight ≥ 45 kg and BMI ≥ 85th percentile(b). BMI will be calculated in the electronic case report form based on height and body weight at screening. * (a) For metformin, a stable dose is defined as at least 1000 mg daily or the maximum tolerated dose for ≥ 56 days prior to screening. For Sodium-Glucose Transport protein 2 inhibitor (SGLT2i), a stable dose is defined as the same total daily dose for ≥ 56 days prior to screening. For insulin, it is defined as the dose ± 25% of that taken at screening for ≥ 30 days prior to screening. * (b) Based on sex-specific BMI-for-age percentiles for the given country or region. If not available for the country or region, the respective charts or tables on cdc.gov may be used. Key Exclusion Criteria: * Female who is pregnant, breast-feeding or intends to become pregnant or is of childbearing potential and not using a highly effective contraceptive method. * Treatment with any antidiabetic or anti-obesity medication (irrespective of indication) other than stated in the inclusion criteria within 90 days before screening. * Known or previous diagnosis of hypoparathyroidism. * Previous or planned (during the study period) obesity treatment with surgery or a weight loss device. However, the following are allowed: (1) liposuction and/or abdominoplasty, if performed \>1 year before screening, (2) lap banding, if the band has been removed \>1 year before screening, (3) intragastric balloon, if the balloon has been removed \>1 year before screening or (4) duodenal-jejunal bypass sleeve, if the sleeve has been removed \> 1 year before screening. * Positive insulinoma associated-protein 2 (IA-2) antibodies or anti-glutamic acid decarboxylase (anti-GAD) antibodies as determined by central laboratory at screening or in medical history. * Recurrent severe hypoglycaemic episodes within the last year as judged by the investigator. * Known hypoglycaemic unawareness as indicated by the investigator according to Clarke's questionnaire question 8. * Uncontrolled and potentially unstable diabetic retinopathy maculopathy. Verified by a fundus examination and optical coherence tomography (OCT) assessment performed within 90 days before screening or in the period between screening and randomisation. Pharmacological pupil-dilation is a requirement unless using a digital fundus photography camera specified for non-dilated examination.