It would be offensive to adults to be treated as children, however some dementia patients are spoken to in that fashion and it can be harmful, according to the Daily Mail in "Don't call me sweetie! Why we should never use 'elderspeak' to talk down to dementia patients."
Elderly people with dementia are often talked to in a form of baby talk, that researchers have dubbed "elderspeak." It is common for dementia patients to be called names such as "sweetie" and "dear."
While the speaker does not mean any harm, it can be harmful to the patients.
Talking to dementia patients in that way comes across as patronizing and may increase their feelings of isolation. It can worsen their problems.
This is something that caregivers and elder law advocates should be aware. It is important to know that it can cause problems for the elderly and we should treat them with respect and dignity.
Reference: Daily Mail (March 24, 2017) "Don't call me sweetie! Why we should never use 'elderspeak' to talk down to dementia patients."