Not for fans of the books; for preschoolers only.
You're right. Even though the cubs are 10 and 8, this show will only appeal to preschoolers. While it is possible that kids who've read or listened to the books when they were younger and those who still like the books when they're of school age will like this series, don't count on it. Take the episode at the amusement park. Brother Bear, age 10, wants to ride the roller coaster initially but ultimately decides not to. This is an excellent indication that this show is for preschoolers and will likely not appeal to an older child. If this show would've been meant for all ages Brother Bear would've gotten on that coaster! For preschoolers, however, while the lessons and values are sometimes too black and white, both are nevertheless good and age-appropriate.