Free apps entice us with the promise of mobile fun at no cost. But it doesn't usually work that way. Most "free" apps have a way of making money, and that way is not always good for kids.

In some apps, the price for free is in-your-face marketing. That means kids are bombarded with banner ads for a variety of products and/or enticed into downloading dubious games as a "reward."

Another form of free apps is called freemium. In this model, you can play the game for free, but the gameplay is set up to get frustrating unless you buy your way out of difficult or time-sucking situations.

The better route to go when kids are involved is free apps that are genuinely free or apps that provide some content for free and then offer more as an in-app purchase presented only to parents. That way kids can enjoy a free app without suffering through hidden or aggressive in-app marketing.

Here are five apps that use that better route â€" they are truly free and good for kids.

NFL Play 60 [1]

(American Heart Association, best for ages 4-up, Free, iPhone, iPod Touch, iPad)

Rating: 3.5 stars (out of 4)

Combining real exercise with an endless runner app, The American Heart Association, in conjunction with National Football League, has created a free app that gets kids moving. To make their character run on the screen, kids have to actually run in place and jump while holding their device. Kids earn coins by tilting the device to shift their running character onto different paths. The goal is to run as far as you can without being stopped by an obstacle. By copying the gameplay made popular by well-known endless runners such as Temple Run and Despicable Me: Minion Rush, kids will be drawn to the gaming while getting fit.

Awesome Eats [2]

Whole Foods Foundation, best for ages 6-up, Free, iPhone, iPod Touch, iPad

Rating: 3.5 stars

Foods become characters in this fast-paced game about sorting, stacking and packing veggies, fruits and recycling. Sandwiched between fun puzzle levels about flinging anthropomorphized food onto the correct conveyor belt are messages from the Whole Foods Foundation about healthy eating. This app is a winner because it combines quick thinking and fast food flinging into a game that imparts healthy advice.

Alien Assignment [3]

Fred Rogers Center at Saint Vincent College, best for ages 4-8, Free, iPhone, iPod Touch, iPad

Rating: 4 stars

Want to get your kids up and moving? This app incorporates an old-fashioned scavenger hunt into a wacky adventure with aliens. When an alien family crash-lands on Earth, your child helps them by taking actual photos of things requested by the alien's computer. The computer may need to see something with wheels or an item you can see through. The app cleverly weaves in the parent's participation by asking the child to "show your grownup" th e pictorial solution before turning it over to the aliens. This app encourages family play time and challenges players to look at everyday objects in a new way.

Endless Reader [4]

Originator, best for ages 4-7, Free, iPhone, iPod Touch, iPad

Rating: 4 stars

High-energy monsters run across the screen, depositing hilariously animated words to start kids off on the path to reading. Kids select a word from within a monster's month, then the word appears as if it were a character. For example, with "d-o-g," the "d" has a face and the "g" has a tail. As players drag the letters to spell the word, the animated letters make their le tter sounds. Next, the monsters rush through the scene, delivering a scattered sentence with the word in it. After kids drag the wiggling words back to the sentence, a charming monster appears to act out the sentence, thus teaching kids the meaning of the word.

If your child has fun learning the first six words, you can purchase more words in three packs for $2.99 each in this try-before-you-buy app. Endless Reader is an excellent educational app with no ads or social media links and in-app purchases that are secured behind a parental gate.

Duolingo â€" Learn Languages for Free [5]

Duolingo, best for ages 10-up, Free, iPhone, iPod Touch, iPad, Android [6]

Rating: 3.5 stars

If your family wants to expand its foreign language abilities, this free app should be your first download. Offering Spanish, French, German, Portuguese, Italian and English, Duolingo provides players with a certain number of hearts per lesson and lets you continue until you screw up enough times to lose your hearts. The lessons are broken into small bits, and they intermix verbal repetition, choose the correct answer, fill-in the blank and spelling practice. While free, you must sign in using an e-mail or Facebook account to use this service. This app earns its money by using your learning to help translate webpages submitted by paying customers.

Jinny Gudmundsen is the Editor of www.TechwithKids.com [7] and author of iPad Apps for Kids, a For Dummies book. Contact her at techcomments@usatoday.com . Follow her @JinnyGudmundsen [8] .