I haven't seen the original Child's Play in years, so I don't remember why Chucky was killing back then. Wasn't it because he was possessed with the spirit of a serial killer? I'd like a simple and emotional premise, like if Chucky was killing every significant person in that boy's life. Chucky wants his new "best friend" all to himself. Even "innocent" things like making his friend feel better. Maybe mom has a new boyfriend, and the boy doesn't like him so he vents to Chucky because his mom wouldn't listen...then Chucky "fixes" the situation by ending the guy's life.
Some AI's are incredibly advanced, down to reacting to situations with all of the intricacies that a person would, and feeling "real" emotions. Hopefully Chucky's advanced tech goes haywire. He needs a warped personality for an AI, meaning imperfections like losing his temper would be attributed to him "glitching". That way we could get some real "human" emotions out of Chucky, which would be intermixed with truly cold moments that only an AI could provide. Chucky should treat these murders like a child playing with toys or living out boyhood fantasies. I want a scene where Chucky and his friend are watching Home Alone, with Chucky sitting there blankly taking it all in; forming his own warped version of the movie in his head, with deathtraps like what we saw the mom stuck in at the end of the trailer. Let's have the boy watching some horror movies and playing violent videogames too. All of that would make a lasting impression on Chucky, giving him a penchant for murder. That's what real-life parents fear would happen to their kids if exposed to those types of movies and videogames, anyway.
We've seen children swear in movies all the time, and a few times, it has been due to them hearing it from a parent or watching television. Chucky should pick up the concept of swearing from hearing the adults around him and what he's seeing on tv; maybe he even picks it up from the boy, who feels safe swearing around his new Buddy. Children curse to each other in real life, but most of them try their best not to do it around adults.