When I was a kid, I used to love to play with windup toys. I'd crank them up and watch them perform. Didn't matter what they did ... clap cymbals together, whatever. It wasn't what they did that interested me. No, what I liked was when they started to run down. They'd get slower and slower, and I'd imagine them begging me to wind them up again before they quit, but I never did. I wanted to watch them die. And in my little kid mind, that's what was happening, not that they were toys who ran down, but that they were things I knew that died. I'd even feel something resembling sadness when they quit moving. And then, if I wasn't too bored, I'd wind it up and start all over again. It wasn't about me ... it was about the toy, about the fading away.
The Toy Story franchise is not about kids, other than as objects of toys' affection. The movies assume that kids will grow up, that they will find new toys to play with, that they will eventually outgrow toys completely. The Toy Story movies tell the tale from the point of view of the toys. Andy is a young boy in Toy Story, by Toy Story 3 he is going off to college. We barely ever see Andy, or any other humans. Andy exists to illuminate the lives of his toys.
And the biggest fear of a toy is that they will be abandoned, that their person won't play with them anymore, that they'll get stuffed into the corner of a closet. Or worse ... the incinerator scene in Toy Story 3 is one of the most terrifying things you'll ever see in a "cartoon".
Toy Story 4 suggests that there can more things to aspire to than being some kid's toy. The need to belong is intense. It's pretty much the emotional basis of a toy's life. And you are always at the mercy of your boy or girl. This feeling doesn't disappear in Toy Story 4 ... much of the plot revolves around attempts to pair toys with kids. But alternatives also present themselves. Woody, the exemplar of the toy who does everything for his owner, decides to join his love, Bo Peep, to find new owners for stray toys. He finds meaning not through a human, but through a fellow toy.
This is perhaps too much to dump on a cartoon designed to make billions. It's more important to note how good Toy Story 4 is, how efficient the animation remains, how the voice actors have created full-blooded characters over the four movies. It's also important to note that Toy Story 4 is often funny, which you might not get from all my blathering. (My wife laughed out loud when the cat barfed up a hair ball.) You can just sit back and enjoy the movie ... deep analysis isn't required. But it's worth appreciating that they have now gotten through three sequels and still haven't let the audience down. That's quite an achievement.