Summer (which has just begun for half the world) is a time for road trips and vacations. That means lots of family fun, but it also means long boring car or airplane rides for the kids, layovers, and waiting in line. Thankfully for parents at their wits end, if you possess an iPhone, you also possess potentially countless hours of free or cheap entertainment to keep your child occupied.

Below is a list of 15 games that are good ways to keep kids busy in the car, on the plane, or while waiting for a table at the restaurant. Many are free or have free versions, and none cost more than $2.99. We’ve broken the list up into 3 sections based on your child’s age, and linked to the free version when available. There are hundreds of iPhone apps that are great for kids, so please feel free to share your children’s favorites in the comments!

Toddlers

Where’s Gumbo (Free/$1.99) – Where’s Gumbo is an interactive storybook that resembles the “lift the flap” board books. The object for toddlers is to explore various scenes and peek behind objects in their quest to locate Gumbo, a lost dog. Gumbo and other animals are randomly placed behind each flap, so the experience is never quite the same each time your child plays.

Memory Match (Free/$0.99) – A simple memory game suitable for kids, Memory Match features fun, kid-friendly animal pictures and is great for toddlers to develop image recognition and motor skills. The free version is ad supported.

Peekaboo Barn (Free/$0.99) – In this educational app, children are asked to guess which barnyard animal is hiding behind the barn doors based solely on the sound the animal makes.

Balloonimals (Free/$1.99) – This is an app that absolutely delights little kids. Children blow into the iPhones microphone to inflate their balloon and shake the phone to assemble an animal, then they can interact with it by petting it and making it do tricks. The free version comes with T-Rex.

Colorama ($0.99) – There are a bunch of coloring book apps to try on the iPhone, but Colorama, which comes with 53 drawings for kids to color in countless ways, is one of the best. Finished colored-in illustrations can be saved to your iPhone’s camera roll so they can be emailed.

Younger Kids

Dizzybee (Free/$2.99) – Dizzybee is a fun and unique accelerometer game in which players are challenged to help Dizzybee solve puzzles and overcome obstacles in order to save his fruit friends.

Brain Toot (Free/$0.99) – This is a fun brain training app, filled with educational mini-games designed to exercise your neurons. Brain Toot, because it has some math games, is probably only suitable for children who have reached a certain point in their schooling.

Topple (Free/$0.99) – Topple is a stacking game. The goal is to stack pieces as high as you can before the time runs out. The higher you go, the more precarious your stack gets, and the pieces have funny facial expressions that give you clues as to how you’re doing. Topple is free, but the second version (Topple 2) is 99 cents.

Scoops ($1.99) – Another stacking game, Scoops differs from Topple in that it uses the accelerometer and has tilt-based controls. Try to keep your stack of ice cream scoops growing, but remember to avoid the falling onions!

PopMath ($0.99) – PopMath is a great educational math game in which players are presented with both problem and answer bubbles. The object is to pop bubbles by touching first the math problem, then the correct answer. Popping bubbles narrows your choices for the remaining problems. The game supports addition, subtraction, multiplication, and division problems.

Older Kids

Word Scramble (Free) – Scramble is a great free game from Zynga, which if their menu screen stats are accurate, has over 1.5 million players. The game is a simple word search — race against the clock to find as many words (of at least 3 letters) as you can. Longer words score more points. The game has a “play and pass” mode, so two or three kids could share a single iPhone and play against one another.

Sudoku (Free) – I never could get into the Sudoku craze, but many of my friends spend hours a week solving them. I’m told that the free Sudoku app from Mighty Mighty Good Games is one of the best.

Bejeweled 2 ($2.99) – The beloved classic gem-swapping puzzle game Bejeweled is even more fun on the iPhone. Something about clicking the jewels with your fingers and actually swapping them with a swipe motion gives the game a visceral feel that it previously lacked. The graphics are also great.

Flight Control ($0.99) – Flight Control is a really fun little puzzle game in which players are challenged to direct air traffic and land planes while avoiding crashes.

Pandora (Free) – Unlimited custom radio stations. Need we say more? The Pandora iPhone app + headphones = hours of silent bliss during long car rides (just stay out of 3G deadzones!).

What other applications do your kids enjoy? Let us know in the comments.