There isn't a single, universally accepted "online text" for 6th-grade History Alive! History Alive! is a series of textbooks published by TCI (Teachers' Curriculum Institute). While TCI *might* offer some online resources for teachers and students who have purchased the physical textbooks (like supplemental materials or online quizzes), there's no freely available online version of the entire 6th-grade textbook.
To access any online materials, you would need to be a student at a school that uses History Alive! and have access granted through your school's learning management system or directly from TCI. There's no public, open-access digital copy.