Factual error: In the scene where Trey's father shoots at the burglar the gun punches baseball sized holes in the door. A .357 Magnum bullet going through a thin wooden door would just punch through, without expanding or tumbling, and leave a hole only a bit larger than the bullet diameter.
Factual error: When Furious goes to the open land with Ricky and Tre to give his speech about his job, it's mentioned about that location they're at being in Compton. They are at the bottom of a hill (due to the slanted street angle). There are no hills in Compton. Also a 27th St. Sign is visible. There's no 27th St. In Compton either.
Factual error: The police cruiser pulling up to Furious' house in 1984 is a 1986 Chevy Caprice.
Answer: It was never said what they stole, just that they were going to go to the store (probably a corner store or convenience store) and they probably stole food. They got caught because they were just kids and not good at stealing or being sneaky. However, they didn't get a 7-year sentence for the theft. It's just that the film jumps to 7 years later and Darrin is now a gang member who has been in and out of jail the whole time. He's just celebrating his release from prison for a different, unknown crime. Chris is in a wheelchair due to a gun shot wound, though it's not stated how or who shot him.
Bishop73
I wouldn't be surprised if Chris shot himself with the gun he alludes to having earlier on in the film when they are still children.