I have little experience running tabletop games for children. However this Christmas as a small gift I ran Hero Kids for a group of six year olds.(my cousins kids) It was a blast and they loved it! Hero Kids keeps it really simple to start with and is a great spring boarding experience for kids role playing. I highly recommend. Great post as well I love seeing more people try this with the younger audience!
https://herokidsrpg.blogspot.ca/