How do I know if my chubby child has diabetes yet?

Age??? Diabetes comes in 2 basic forms. The children's form develops abruptly after a virus destroys Insulin production.They quickly loose sugar in the urine, eat & drink ravenously & loose 10lb in a week. The fluffy adults make Insulin but not enough and they gradually get into trouble over months or years.A glucose tolerance test or A1c can give you early indication on a teen, in pre teens a urine test.
Blood test. American diabetes association recommends children with bmi (body mass index) over 85th percentile for their age and gender be screened for early sign of diabetes. Glucose tolerance test and/or hemoglobin a1c are often checked.
More important tests. If you are going to poke your child for blood, ask that several important things be included to test blood fats, kidney, liver and thyroid as well as blood sugar: hga1c, fasting blood sugar, creatinine, bun, lipid panel, ast, alt, tsh. And do get your child's blood pressure monitored.