There’s a new type of game that’s becoming increasingly popular for kids and families. You don’t have to pay any money up front and there are hours of fun to be had inside each title. But there’s a dark side to these games that has the potential to drain your savings faster than you can spell the word “free”.

Appearing on smartphones and tablets, “freemium” games offer a premium gaming experience without any immediate cost. Many of these titles are developed by major publishing houses and feature 3D graphics, cute characters, and quirky art that makes the title seem truly unique.

But these so-called unique titles all have one thing in common: they’re all designed to make money, even if you’re getting a game experience that arrives with a zero dollar initial price tag.

Most freemium titles rely on the principle of time. The games work like this: you want to play the game, but every move you do takes a specific amount of in-game time. Perhaps there’s a 15 minute recharge on a spell, or a 30 minute build time on a house. These are real-life times, minutes that you could normally close the game down and go do something else, like that work you keep saying you’re going to do, or the homework you’ve been nagging the kids to get done.

Buying more gems let you do things without waiting, and these can be costly. Buying over 3,000 gems in one hit will cost you a real world sum of $109.99 in the online world Dragonvale.

But kids don’t want to wait, and who can blame them: they’re kids. Most of these titles allow you to speed up these sections by a quick and simple purchase using in-game coins, a monetary system that – while virtual – buys faster gameplay. These purchases also buy extra in-game assets such as new rides, spells, weapons, and anything else that can make your game appear better.

While you’re given an initial burst of virtual money to play with, these coins will run out if you want to play the game quickly. So what do you do? Just like in real life, you need to go out and get some more.

Every freemium title comes with a basic amount of free play, but if you want to progress at a faster rate, you’ll need to buy some in-game additions, and these cost real money.

“Dragonvale” is one such game, a title that tasks you with raising cute little dragons for a zoo. Playing the game takes time, but if you don’t want to wait, you don’t have to. You can speed it up with coins, and once you run out, you can buy more coins. Lots of coins. And food. And gems.

All of these extras cost money, real money. The money that you work for in your day job, the money that you can buy real groceries with. This money buys you digital money – coins, tickets, gems, food – inside of a video game, allowing the freemium games to be played at the same speed as a regular purchased outright game.

Some of these apps warn about in-app purchases from the first play, but that warning only pops up once.

The difference here is that the costs can add up, creating an amount that accounts for a cost far higher than any full-price game would ever cost.

In one such instance, a GadgetGuy reader racked up a debt of over $1000 as their child continually purchased packs of virtual items, unaware that the money was adding up in their iTunes account.

EA’s modern version of its classic “Theme Park” game franchise which launched only a few months ago comes with the same design. In this title, you can buy more attractions and rides to stick in your virtual theme park, and to get them quickly or to grab special rides to make your park better, you’ll want to reach for the wallet.

Building your own virtual theme park was never this costly.