My mother-in-law had dementia and of the daughters-in-law, it fell to me to step in when a caretaker besides her regular one was needed.
I NEVER would have dreamed of being condescending to her, even though it was necessary to make sure I was very clear about things, that I had to simplify instructions and take things one step at a time and speak slowly sometimes and patiently explain what was going on for the fifth time in as many minutes.
Dementia patients cannot help what is happening to them and in their more lucid moments know it and hate it. I don’t think it helps at all to treat them as any less than adults, even when you have to relate to them at a level a child would understand.