Meditation for kids of all ages can be different than it is for adults. The biggest difference is that the duration is shorter. Adults in most cases have more patience and can rely on their focus more as the time extends and things get more difficult. Adults can also grasp the concept of self reflection better. Typically with kids, you need to stay focused on smaller periods of time or chunk that time out into blocks, with breaks in between.
At the start, kids won't understand why they are meditating or the benefits. Likely, they'll perceive it as boring or difficult after a few mindful breaths. A good way to approach this is to introduce the practice of meditation through toys, stories, crafts or movement exercises.
There are numerous benefits for children who meditate: quiet calmer children which transforms the environment into a more peaceful area. Meditation also has many of the benefits in children as it does in adults: better sleep (which is critical for children), sharper attention, increased focus, more creativity and enhanced mood control.
The best time to teach children to meditate is when they are calm and relaxed, which lends itself to either a morning route or bedtime. Sitting with a child of 4 or 5 years old and going through some simple breathing techniques can be something they can feel in their bodies.
Guided imagery is a very effective technique to help with a bedtime meditation routine. There are apps such as Headspace and Calm that provided recorded, bedtime programs for meditation, with kids options provided in them. Breathing techniques for young children can setup them up with a strong foundation for a meditation practice as they grow up. AwakeandMindful.com offers several good meditation videos for kids.
Preschoolers right up to teens can learn how to meditate. They may need some guidance at first, but once you help them with the training wheels, they will learn to do it on their own. Giving them ideas on tools, such as breathing focus, imagery, apps or a simple timer can allow them to craft and hone their meditation routine to a level of comfortability and make it repeatable.