“How young can a child get diabetes?”

Rarely, an infant can get diabetes. Diabetes is most commonly manifested with "growth spurts" like at 6 years old and twelve years old. So, 11, 12, 13, and 14 are very common times for diabetes to become manifest. Usually weight loss at that age is the common manifestation of diabetes. That with increased thirst and urination (not the weigh gain).

Any age. Children that have DM, if type I may have weight loss problem. Symptomatic type II DM can have weight loss also. Not sure what you mean by homeschooling. However, majority of the children that have been doing virtual schooling gain weight due to inactivity and frequent snacking or drinking. Please check with his doctor.

It depends. Type 1 diabetes mellitus can affect kids as young as 1 year old. On the other hand, Type 2 diabetes mellitus used to be associated with weight gain during adolescence, but lately has become more prevalent in overweight kids as young as 8 years old.

You can get it at any age. I have a child as young as 3 mo. old develop Type 1 diabetes (T1D) & 4 yrs. old with Type 2 diabetes (T2D). There several forms of a disease called "Monogenetic Diabetes" that can appear in newborns. Since your sons problem is wt. gain, if he has diabetes it would be T2D since people with T1D usually lose wt. I doubt though that your son has diabetes since you didn't mention any of the other symptoms. Children who are home schooled do frequently have wt. gain due to overeating & under exercising (no recess or gym classes) just as adults quarenteened at home with the Corono-virus have gained an average of 8-10 # in just a month or so at home. For the wt. gain please see a Dr. for a test for diabetes or get a urine test kit at the pharmacy & test his urine for sugar & ketones. If positive see a Dr. right away. If negative you may still want to see a Dr. as the wt. gain can lead to insulin resistance that can lead to T2D. I don't think he has diabetes but see a Dr. anyway about his wt. gain & correct that since obesity can lead to a variety of other complications (heart & others).