I'm offering some unsolicited advice today. Free of charge. You're welcome.
Never, EVER, put a four-year-old child in a position where they feel like it's necessary to scream at the top of their lungs.
At four years of age, children have a large lung-capacity and strong vocal chords.
It is loud and embarassing and a downright painful experience for everyone involved.
Any child confronted with the reality that they're about to get four shots at their four-year-old checkup... well, they're bound to feel like they need to somehow vocalize their objection.
And it may seem like the longest 3-4 minutes of your life when you have to hold them still during the process and calm them down afterward.
I will say that the promise of stickers and donuts seems to have a calming effect.
(For both the grown-up and the preschooler).