My kids have really been enjoying the
Magic Tree House books. It gives the kids an immersive experience into the past. The books do feature a bit of magic, so if you're wanting to give them objective history, you'll want to discuss what's magical and what's not.
Some of the books are a bit too exciting for my kids, especially before bed. Reading about escaping Pompai or being lost in a haunted pyramid are a bit terrifying for my kids, so we've had to switch to reading them during the day rather than before bed.
(Another mild complaint is how much the characters complain about wool being hot and the girl, Annie, complains about stays and wool dresses as making movement hard. There's a reason people wore wool, and it's a very breathable fabric!)