FreeTypingGame is a nice option because it has three clear sections for lessons, games, and tests. This way, your kids can learn from the lessons, practice their skills with nifty games, and then take a quick test to see how well they are progressing.
The lessons let you choose from 30 options based on the keys to be learned. Plus, you can pick a goal such as achieving 20 words per minute. Cool game themes include everything from frogs on a diet to saving sailboats and allow you to choose the related lesson as well as the difficulty level.