Josh Lacey 
Time Travel Twins: The Stone Age Clash [EPUB ebook] 

Discover two sides of history with the Time Travel Twins!Twins Scarlett and Thomas are learning about the Stone Age, so Grandad lets them use his time machine. Thomas wants to see a sabre-toothed tiger; Scarlett wants to see Stonehenge. They were thousands of years apart, what should they do? Go back in time twice of course!From perilous encounters with Neanderthals and woolly mammoths, to being roped into a mysterious ancient ceremony, the twins will need to keep their wits about them to survive their visits to the Stone Age!Also in the series: The Viking Attack The Roman Invasion