Calm.com – This is an amazing app and website for kids and adults. There is a limited amount of meditations for free and an option for a subscription. While the subscription is a bit pricey, it is completely worth it!
Insight timer – another great app for guided meditation, but even better as a meditation timer. Great to use in the classroom if you are starting your class with a mindful minute.
http://annakaharris.com/mindfulness-for-children/ – This site is great to use with kids. I have used the activities with my students. They are shorter and are a great way to introduce students to mindfulness activities. Students can also use their own devices to do the activities at home.