Do you want carrots cooked before juicing?
You can directly tie the juice and add some boiling water, which should be no problem. My baby drank this way when he was 4 months old. Sometimes give him egg yolk to drink together, and the baby likes it very much. If you are afraid of diarrhea, you can cook it and mash it for him. In fact, the baby is not as easy to have diarrhea as we thought, so you can add less for the first time.