The following are five of the best websites on the Internet that are the most useful for either exposing your kids to the Mandarin language, or for supplementing Mandarin lessons.
One of the best website for exposing your children or your students to Mandarin is Poisson Rouge. Poisson Rouge looks just like any other children's site on the Internet, complete with fun cartoon pictures and animation.

Pousson Rouge Main Page
The one big difference is that when children start clicking around on different parts of the picture, images come to life, and a narrator says the word of the object that the child clicked, in Mandarin.

Exploring Pousson Rouge
Each section of the site consists of an entire virtual world with common objects grouped together, such as the "transportation" page. This is where children will learn how to say words like bicycle, tractor, boat or airplane.
Clicking on the next page, children will learn all about animals.

Learn Animals in Mandarin
Once the child is done playing on each page, they can click on the small picture for the next page in the corner of the screen to continue. There are lots of areas to explore, and the fact that there are no actual text words means that children can focus on learning how the words for different objects are supposed to sound, rather than getting distracted by the text.
One of the most unique sites for learning the chinese language is Semanda. This website focuses on the tried and true method of learning language through memory and repetition - flashcards.
The nice thing about this interactive site is that the collection of flash cards is customizable as far as content goes.

Learn Chinese With Flashcards
Choose from word types such as animals, nature, weather & space and lots more. Once you make your selection, just click "OK" and the flashcard slideshow will appear.

Using the Flash Cards
For each flash card, you will try to remember how to write the given word in Mandarin. Then click on "Flip card" to see the correct answer. Each card also features a picture of the object as well. Just click "Next card" to work your way through the flashcard collection.
Another great site is known as the Chinese Outpost. This site isn't so much a place for kids to go for strictly learning Mandarin - it's more of a resource for really digging into the language and understanding its nuances.

Understanding the Language
This is where you can go for a Mandarin Tutorial that explains things like the tones of Mandarin Chinese. At this site, you can also use the dictionary, browse the other learning resources and even read China news.
The website professorgarfield.org offers free online cartoon e-books in several languages, including Chinese. You can read the books on screen, or have them read out loud to you in Mandarin. This is great for kids who already can understand some Chinese. The same ebooks are also available in English.
Mandarin e-Book for Kids from the Professor Garfield Toon Book Reader.
If your child or student is more inclined to learn language better through the use of multimedia, then this website should be on your list.
While eChineseLearning sounds a little bit cheesy, it actually has some great resources for kids that are interested in learning to speak Chinese.
The "Chinese for Kids" section is divided into three sections, one for each level of learning. Each topic within these levels is actually comprised of videos in Chinese, which are broken down underneath the video in transcripts made of up sentences.
eChineseLearning Videos
This allows kids to read each sentence, one at a time, and then click the play button to hear the sentence spoken. This improves move the ability to read the text, as well as understanding how to correctly pronounce the words.
They say that if you really want to learn a language, the best way to do so is by immersing yourself into the culture itself. This is why it makes sense to visit the Chinese.cn website on a regular basis to take advantage of the learning resources there created by the Chinese.
Remember to Visit Chinese.cn
This website is laid out in a blog format, but once you start clicking around, you'll see just how loaded it is with valuable resources and information. Kids can make use of the Chinese Wordbook to see the 800 characters most often used in Chinese daily life, or teachers can make use of the Flash Card utility to create Chinese cards for the classroom.
Many people think that learning Mandarin Chinese is very difficult and overwhelming. The truth is that while it is certainly one of the more difficult languages to learn, if kids get an early start, they will not have a problem learning the language.
And visiting websites like those listed above can certainly help that process along.