My ds was 7y/o on our last visit to WDW, and he had no interest in those particular rides. He was more excited about attractions the likes of Buzz Lightyear Space Ranger Spin, Pirates OTC, Tom Sawyer's Island and the HM.
But he did surprise me and asked to go on the Triceritops Spin at DAK, which is basically the same ride as Dumbo at MK. The advantage, however, was that at DAK there was no wait to get on TS (we walked right on), where as I hear that there is frequently quite a long line for Dumbo.
So, I'd leave it up to the kids to decide which rides they most want to experience. Each member of our family personally chooses one or two 'must see' attractions within each of the four major parks... and we make it our priority to get to those at some point during our visit. As for the lesser priority rides and attractions... we may decide to hit or skip those as we tour each park, depending on the lines and Fast Pass availability.