The purpose of the study is to evaluate the effectiveness of the Happy Bob -application on glycemic control in children aged 9-13 years with type 1 diabetes. Additionally, investigators evaluate the perceived burden on the diabetes treatment to families during the Happy Bob use, compared to conventional treatment (diabetes distress).

This is a prospective, randomized, controlled study where primary endpoint is the change in time-in-range (TIR, 3.9-10 mmol/l) after Happy Bob application initiation. Secondary endpoints are HbA1c, time below range (TBR, <3.9 mmol/l), time above range (TAR, >10 mmol/l), mean sensor glucose (SG), standard deviation of SG, coefficient of variation (CV, SD/SGx100 (%)), number of boluses and diabetes distress evaluated by PAID (Problem Areas In Diabetes for parents and children/youth). A sample size of 40 subjects (20 in each groups, and assumed drop-out rate of 10%) would provide the trial with 80% power and type 1 error rate of 0.05 with the following assumption: 7% higher TIR during Happy Bob -use compared to conventional treatment with continuous glucose monitoring (CGM), with a standard deviation of 7.5% (based on Happy Bob marketing study).

The inclusion criteria are 1) Type 1 diabetes diagnosis more than 6 months ago 2) Age 9-13 years and prepubertal 3) capability to use Happy Bob -app and continuous glucose monitoring (CGM). The exclusion criteria are psychiatric diagnosis and other conditions, which in the opinion of the investigator would put the participant at risk during the trial.

The study includes 6 months study time with 2 standard outpatient clinic visits.

The study will be conducted at pediatric diabetes outpatient clinics of Helsinki University Hospital (New Children's Hospital, Jorvi Hospital, Lohja Hospital, Porvoo Hospital and Raasepori Hospital).

The study protocol is explained to the participants (9-13 -year-old children) and their guardian(s). Informed consent from participants' caregivers and participants will be taken by investigators, clinicians or diabetes nurses. The investigator or his/her representative will explain the nature of the study to the patient and parents, and answer all questions regarding the study. Prior to any study-related screening procedures, the informed consent statement will be reviewed and signed and dated by the participant's caregiver.

The participants are using their usual diabetes treatment (multiple daily injections, MDI, or continuous subcutaneous insulin infusion, CSII) with Dexcom™ G6 (Dexcom Inc., San Diego, CA) CGM during the study period and will get instructions for insulin treatment from their diabetes nurses/doctors as usual. Study group will also use Happy Bob application, which takes data from Dexcom CGM system, and gives a user a star, whenever he/she is within target area, measured every five minutes. The more stars patients get, the better the score is. Happy Bob is not a medical device, and it does not give any instructions on how to dose insulin. The use of CGM is familiar to subjects and their families, since every patient is already using some CGM before the study. If Dexcom CGM is not the CGM device patients uses normally, the instructions for the use is given by study nurses either remotely (video appointment) or during outpatient clinic group visit.

The instruction for the Happy Bob use is given by study nurse in groups, either remotely (video appointment) or in outpatient clinic group visit.

The used CGM is Dexcom G6 sensor, which is integrated to Happy Bob -app. It measures the glucose level in the subcutaneous tissue. The CGM sensor connects to a transmitter that sends the glucose data to patients phone (Dexcom app) and receiver device. The sensor is worn for 10 days and then replaced with a new one by the patients' caregivers. The CGM data are collected from Glooko® Therapy management software, which is in clinical use at Helsinki University Hospital. The data from CGM is downloaded either by caregivers or diabetes nurse at diabetes clinic.

Glycated haemoglobin (HbA1c, mmol/mol) (Afinion2™, Abbott) is measured by a diabetes nurse from fingertip as point of care test. The Diabetes Distress is evaluated by a standardized questionnaire (PAID) in run-in phase and at 6 months visit.

The study includes a starting visit, during which Happy Bob and Dexcom G6 CGM is started and patient's normal outpatient clinic visits in 3 and 6 months.

Inclusion Criteria:

• Type 1 diabetes diagnosis more than 6 months ago
• Age 9-13 years
• Prepubertal
• Capability to use Happy Bob -app and continuous glucose monitoring (CGM)

Exclusion Criteria:

• Psychiatric diagnosis and other conditions, which in the opinion of the investigator would put the participant at risk during the trial.