In a classic experiment, rats were placed in identical cages. Each cage had a bar that could be pressed down. In cage 1, pressing the bar resulted in food being dispensed, every time. In cage 2, pressing the bar resulted in nothing happening. In cage 3, pressing the bar resulted in food sometimes being dispensed and sometimes not being dispensed in a random fashion.
You have probably guessed which bar was pushed the most – the bar that randomly dispensed food. We humans are not rats and we humans respond to rewards differently than rats – or do we? If you want your child to continue a behavior, praise them randomly. If you want your child to stop doing something, try ignoring the behavior. If you praise them every time they may simply come to expect it.