Diabetes is covered by the Equality Act 2010, which makes it illegal for employers to refuse a job to someone simply because of their disability. As a result of this act, people with diabetes 
can no longer be banned from a particular role simply because they have diabetes; instead their fitness to do the job must be individually assessed. The only employer exempt from the Equality Act is the Armed Forces, where a blanket ban on recruiting people with diabetes still applies.
Some jobs have strict medical standards that people with diabetes may not be able to meet. These usually apply where a job is unusually risky, eg because it involves operating heavy machinery or vehicles. The most common reasons for people with diabetes not meeting medical standards is the risk of hypos. In most jobs a hypo doesn’t pose a risk to others, but in some situations it could. For example people with Type 1 in the UK are not allowed to become train drivers or commercial airline pilots.
It’s not fair
Sadly, despite the legislation, some people with diabetes still experience discrimination. If your child is fit to do a job but thinks they’ve been refused because of their diabetes they are likely to have rights under the Equality Act.