Birth - 1 year: Essentially a small cute animal. Handle accordingly; gently and affectionately, but relying heavily on the caregivers and with no real expectation of cooperation.
Age 1 - 2: Hates you. Hates you so much. You can smile, you can coo, you can attempt to soothe; they hate you anyway, because you’re a stranger and you’re scary and you’re touching them. There’s no winning this so just get it over with as quickly and non-traumatically as possible.
Age 3 - 5: Nervous around medical things, but possible to soothe. Easily upset, but also easily distracted from the thing that upset them. Smartphone cartoons and “who wants a sticker?!!?!?” are key management techniques.
Age 6 - 10: Really cool, actually. I did not realize kids were this cool. Around this age they tend to be fairly outgoing, and super curious and eager to learn. Absolutely do not babytalk; instead, flatter them with how grown-up they are, teach them some Fun Gross Medical Facts, and introduce potentially frightening experiences with “hey, you want to see something really cool?”
Age 11 - 14: Extremely variable. Can be very childish or very mature, or rapidly switch from one mode to the other. At this point you can almost treat them as an adult, just… a really sensitive and unpredictable adult. Do not, under any circumstances, offer stickers. (But they might grab one out of the bin anyway.)
Age 15 - 18: Basically an adult with severely limited life experience. Treat as an adult who needs a little extra education with their care. Keep parents out of the room as much as possible, unless the kid wants them there. At this point you can go ahead and offer stickers again, because they’ll probably think it’s funny. And they’ll want one. Deep down, everyone wants a sticker.