Place the foil packets in a single, snug layer in the bottom of your slow cooker, seam sides up. It’s fine if they lean against each other a bit, but try not to stack them.
Cover the slow cooker with the lid and cook on LOW for 3 to 3 1/2 hours, or on HIGH for about 1 1/2 to 2 hours, until the cake portion inside the packets feels set and springy when you gently press the top of a packet with a spoon.
Turn off the slow cooker and let the packets rest for about 10 minutes. This helps the hot filling settle and makes them easier to handle.
To serve, leave the packets in the slow cooker for that fun reveal. Place a dollop of whipped topping right on top of each closed foil packet, then use tongs to carefully lift one onto each plate. Let everyone peel back their own foil to reveal the warm strawberry cake inside, then scoop through the whipped cream into the dessert. Serve any extra whipped topping on the side.
For picky eaters or different tastes, you can swap the strawberry pie filling with other flavors like cherry or blueberry, while keeping the same 4-ingredient idea. If you’d like a little brightness, stir a teaspoon of lemon juice into the strawberry pie filling before spooning it onto the foil. To make smaller kid-sized portions, cut the foil into smaller squares and use a bit less filling and crumb mixture in each packet; kids love having their own mini dessert to open. For a slightly richer flavor, use a butter or vanilla cake mix instead of plain yellow. If you don’t have canned whipped topping, you can use a can of spray whipped cream or quickly whip your own heavy cream with a bit of sugar right before serving. These packets are best eaten warm the day they’re made, but leftovers can be cooled, stored in the fridge in their foil, and reheated gently in the slow cooker or oven until warmed through.