First, my thoughts on the game itself: The art and general theming is super charming and the gameplay is really fast paced and fun! I think using candy as both the ammo and health is really interesting--I've toyed with concepts like that myself--but once you get >100 candy, you start feeling kind of invulnerable. I think if the enemies were more deadly it'd effectively balance things out. Regardless, super fun game and you did a great job!!
Now, here is my ultimate SPOOKIE guide: When you start, focus toddlers above everything else. They take the least candy to dispatch and their drop rate is high enough to propel you through the early game. 8th graders can mostly be ignored early on and teenagers are infrequent enough to just take care of upfront--adults, on the other hand, can actually be used to farm candy if you're not dealing with anything else. Adults should absolutely be killed when they are found in clusters of enemies, however! Once you get around 200 candy, you can mostly just circle around the enemies as they congregate in the center of the map, which makes them an easy target. You should be able to continue like this all the way up to when you max out on candy (800), at which point there are so many enemies that it's best to keep circling, wait for a multishot powerup, and then wipe them out. You should be able to sustain yourself with this strategy for quite a while :]