Here's a subject that's close to my heart, not only because I have a child but because my mother has done quite a bit of work in this exact field: reducing pain and fear in childhood injections. It's very doable: it has to do with how you talk about the shot and how you administer it. (Child in lap, breastfeeding if young enough. If older, give them the tools to distract themselves.) There's a lot of exciting work in the field of child's pain that's coming out of Canada, including this video, which demonstrates that shots are possible without a lot of tears.