There is a fine line here. Fluctuating blood sugars can make them very moody and feel like crap. Juvenile diabetes does effect their moods. Which comes first, the chicken or the horse? While I agree that diabetes should not be used as a crutch, it is entirely possible that you are BOTH right, i.e., sometimes her moods are caused by her blood sugars, other times not. Who is the primary caretaker of the child? Are you the primary caretaker? Or is her father and grandparents the primary caretaker? You may have a valid point and should talk to a family therapist. You will need to have understanding as to how fluctuating blood sugars, up and down, hour by hour, effect mood, even though at the time of the blood sugar check, her sugar is “normal.” You also need to understand insulin on board. A “normal” blood sugar could be normal upon blood sugar test, only to plummet to 50 shortly thereafter, and yes, they will be moody, it may be a sign of a quick drop. Alternatively, that normal blood sugar could be cycling upward very quickly to a high sugar, in which case moodiness is also a sign. Three year olds are very temperamental in general. A three year old who is having to live with constant injections and frequent blood sugar checks has much more to deal with than a non-diabetic child and should be given some room to express her feelings. But I would feel free to say No if necessary and let the chips fall where they may if you feel the child is being unreasonable when she is in your care. She will probably learn not to pull temper tantrums with you if you do not cave in after a few tries. I would not, however, interfere with her grandparents or parent handling of her or try to take over disciplining the child. Unless you are her primary caretaker, it is not your call. Also, you will need to learn to love this child as your own as your relationship with her father deepens. If you resent the child because of her behavior issues (and I do not believe this is the child’s fault) this could cause trouble for your relationship.