They generally either hang from the top of the trunk lid, or will be located inside the luggage compartment near the taillights. Pull this, and the trunk should pop right open.
If your car doesn’t already have an emergency trunk release, you can buy one online. They’re pretty simple to install, and offer a little peace of mind.
Try the backseats: Many cars have fold-down rear seats. See if you can find a trunk-mounted release for them, or if that fails, just start kicking or pushing against them. This may not work if there’s a couple of Mafia heavies in the back seat.
Look for the trunk release cable: Most cars have a remote release lever or button. If it’s a button type, you might be in trouble here, as they use a solenoid to pop the latch open. Older lever-style ones use a physical cable, and if you can find it, pull like crazy and try to pop the trunk.
Try to force the latch: If you’re like MacGyver, you never go anywhere without your trusty Swiss Army knife. Failing that, feel around for a screwdriver, the tire iron, a prybar, or any other tool you can use to attempt to force the latch with. Some cars even come with a factory toolkit mounted in the trunk, so you might luck out here.
Remove the brake lights: Unless you’re an anorexic supermodel, no, you won’t be getting out this way. However, it will get you fresh air and the ability to signal for help.
The brake light assemblies on most cars can be removed without any tools whatsoever. If you can get the whole thing removed, you can stick your hand out through the hole and wave frantically for help.
At the very least, disconnect the wires — because without working brake lights, the chances of getting pulled over go way up. Of course, getting rear-ended would ruin your day, but that beats the 9mm hemorrhage Gino and Luigi might be about to give you.
Use the jack to pop the trunk: This one is a bit of a longshot, but when you’re facing the wrath of the Corelones, it’s worth a try. If you can pry the thing out from under you, see if you can raise it enough to bust the trunk open.
This is really only a possibility with cars that have classic scissor jacks (the kind that forms a diamond shape)… and if the car is equipped with run-flat tires, I’d be preparing to sleep with the fishes if you’ve already tried everything else.
In real life
In all seriousness, getting stuck in the back of a car can even happen accidentally. In fact, a child being trapped in a trunk is a far greater risk than any kind of kidnap scenario. Heatstroke is one of the biggest dangers.
The NHTSA offers 5 basic tips to prevent a real nightmare, which we have summarized here:
Teach children not to play in or around cars. Make sure they understand that car trunks are for things only, not for pets, not for people — and not ever for playing.
Always supervise your children carefully when in and around vehicles.
If your child is missing, one of the very first places you should check is the trunk of your car, and of all vehicles in the area (neighbors, street parking, etc.)
Always close and lock your car doors and the trunk, and be sure keys and remote entry devices are out of sight and reach of your kids.
Keep the rear fold-down seats closed/locked to keep your children from climbing into the trunk from inside the car.
You will probably also want to make sure you have an escape latch installed, and if your kids are old enough to understand the dangers (and not just be intrigued by the concept), teach them how to use it in an emergency.