It's becoming normal for parents to hand tablet computers to small children to keep them quiet. And studies show that 40-percent of kids under age 4 have used one to play games, watch videos, or use apps. But is it safe to do that? Experts say that's an important question. We already know that TV interferes with play, exploration, and interacting with others - which are the building blocks of learning, and social development. And the more kids watch videos, or play computer games, the more likely they'll develop attention problems later on.But tablet computers may be even worse than TV for kids.Studies show that a young child will look away from a TV screen 150 times an hour. But a well-designed app is more engaging, because it has a touch screen, and the spot that a child touches is often where the action happens. So kids become fixated on the screen. Parents are also finding that kids using tablet computers go into a trance-like state. And it's murder to get the iPad away from the child without a temper tantrum. Why? Because they're becoming addicted. A lot of apps are designed to encourage a child to keep playing by offering rewards or exciting visuals. That produces a squirt of the feel-good hormone, dopamine, just like an addict gets from drugs. So what affect does that have on a kid's mental development? Here's what scientists know: When kids play with toys - say, Legos - they decide what they're going to build, and when they're done playing. But with an app, the game determines what the task is, and when it's completed. And that decreases a child's ability to imagine and create. So you may want to keep your iPad away from your kid, until they're a bit older and their brain is more fully developed.