For that age Susan Wise Bauer's Story of the World is great. K12's history courses for grades K-4 are also wonderful (but more expensive).
For kids working at a 4th grade level or so, I'd recommend Joy Hakim's A History of US, but I prefer the *concise* edition (produced by K12).
And for kids working at about a 5th grade level K12's Human Odyssey series (world history) is truly excellent.
(K12 really has done an amazing job with their history program, at least with the input part.)
Joy Hakim's The Story of Science is good too. I'm currently pairing it with the Human Odyssey.