my wife and while we were getting vaccinated we had them watch and were explaining to them how non painful it is.

My daughter was convinced and she didn't express any fear ( she did shed a tear though after the 1st vaccine tho ).

Had my boys flip a coin to decide who'd go next ( coin flipper app ) and my youngest went next and my wife held him while he was getting vaccinated ( he was making plenty of noise ) and I held my phone with the show Little Einstein playing for him to watch. After my older son saw his other two siblings get vaccinated he had a lot less fear but still sat on my wife's lap while getting vaccinated.

Something that helped motivate them and make it a good experience was we promised them pretzels and icees at Sam's Club afterwards. Not only that we promised to take them to each get a $10 - $15 toy as well.