Lights, camera, action!
We open with two families going through similar predicaments, albeit in radically different ways.
First, we have the Szalinskis. Father Wayne is a scientist who quit his day job to work on an ambitious new invention—a shrink ray—but it's not working out as planned. (It just blows things up.) Because of this, he hasn't been paying much attention to his family, leading his kids Amy and Nick to feel ignored by their old man and forcing his wife to stay at her mother's house for a few days.
Then we have the Thompsons. Big Russ, the family's patriarch, is beyond excited for a weekend fishing trip, but he's pretty much the only one who is. His eldest son Little Russ was recently "cut" from the football team, which angers his former football star father, and his youngest son Ron is a troublemaker who's perpetually pushed to the side.
Fun stuff.
Wayne leaves the house to present his as-of-yet unproven invention at a business conference, leaving his kids to clean up the house ahead of their mom's return later that day. While they do so, Ron accidentally hits a baseball into Wayne's lab, striking the shrink ray and somehow making it work. Russ forces his little bro to go over to the neighbor's house to apologize, and through a crazy series of events, all four kids end up…shrunk.
Ahh. Now the film title makes sense.
After his presentation is a failure, Wayne returns home and smashes his machine to bits. Whoops. To add another "whoops" to the mix, he sweeps up the now-tiny kids and throws them in a trash bag, which he then plops on the curb. The kids manage to escape the plastic bag and begin their long trek across the yard to the Szalinski house.
They endure a series of trials and tribulations, including a battle with a swarm of bees, a sprinkler system-induced typhoon, and plenty of interpersonal conflict. Meanwhile, Wayne finally realizes what happened to the kids and begins searching the yard for them, eventually revealing this to his wife Diane, who joins his search.
The kids befriend an ant—aptly named "Antie"—who they ride like a steed across the yard. Sadly, Antie is killed while battling a scorpion that has attacked the group, reminding us to never stomp on insects ever again. While Diane continues her search for the kids, Wayne gets hard at work at repairing the shrink ray in the hopes of returning them to their normal size.
Ultimately, the kids hitch a ride on Quark, the Szalinski family dog, and make it inside the house. Wayne nearly eats Nick as he floats in a bowl of cereal, but Quark once again saves the day. Good dog.
After testing out the newly repaired shrink ray on Big Russ, Wayne returns the kids back to their normal size and there are hugs and kisses all around. Both families now have a greater appreciation for their bonds, and the movie closes with the whole bunch enjoying a tasty, oversized turkey dinner. Who ever said that science doesn't pay?