Yoga poses for kids are poses that have been adapted to appeal to children. They are poses that inspire the already playful nature of children, and they are poses that children can undertake and achieve success with. In many cases, poses that are difficult for adults are easier for children who don't have the same fear of falling and whose bodies are often more limber. Kids yoga poses may be exactly the same as the 'adult' or 'real' version of the pose, or they may be slightly amended, or undertaken with a different focus- such as howling at the moon in upwards dog and barking in downwards dog.
Either way, teaching children yoga poses early enables them to learn a great deal about themselves and how to interact with the world. The technique of meditation, which is so clearly intertwined with the practice of yoga, has stress relief benefits that may actually help children avoid diseases which are becoming all to common in this day and age. The benefits go on and on, and the downside? Well, there really is no downside for children learning yoga.