YouTube Kids originally launched earlier this year for both Android and iOS devices but for US-based users and it wasn’t available in other countries. It’s designed for the younger audience that wants to go to YouTube to watch videos and provides a safely filtered view of YouTube for younger children with some parental controls. As of today, YouTube Kids is now available in Canada, Australia, Ireland, New Zealand, and the United Kingdom.

YouTube Kids Feature Set

• Designed for Kids: big buttons and easy kid-friendly categories that younger children can tap on. It can also stream to your big screen TV via built-in Chromecast and Airplay support.
• Video Content for Kids: younger children can watch specific shows like Thomas & Friends, Talking Tom, online hits like Mother Goose Club and more or select from their own interests such as sports, animals, gaming, crafts and more. Each localized copy will have curated content for that local market so for example, popular shows in Ireland won’t be the same ones as Canada.
• Built-in Parental Controls: Built-in timer for how long parents would like their child to watch videos for, remove the option to search for videos and just use the built-in categories. YouTube states that not all automated systems are perfect so they allow parents to flag videos they feel are not appropriate.
• Gotchas: the app is free and with many freemium model apps, ads are part of the experience. This is also true for YouTube Kids where some of the content providers will play ads before the video your child selected will play.

You can download YouTube kids by visiting the Play Store for Android devices or the App Store for iOS devices.

Sources: 
http://www.pewresearch.org/fact-tank/2015/02/12/5-facts-about-online-video-for-youtubes-10th-birthday/
http://www.theverge.com/2015/11/18/9754688/youtube-kids-now-available-uk-australia-canada-ireland-new-zealand