We explored the layers of the Earth with playdough. We also read Planet Earth, Inside Out by Gail Gibbons. It was a little long for the attention span of a 6 year old but was interesting. It would have been better to split into 2 parts. The second half covers volcanoes, earthquakes and tsunamis, which would make for a good second lesson.
This is the link that I used for the playdough activity: http://www.123homeschool4me.com/2014/05/earth-science-experiments-for-kids-1.html?m=1