I was there with my seven year old, he did all the blues first day, went back later in the week and did Cylimm Coch (sp…. its the one with the little fox on it) which was a 12K loop, difficulty was just a step up from the blues, a bit steeper down, and a little rougher, but still all good for kids. There were one or two fire rod climbs that he didn’t have the endurance for, so we walked some of those, but he rode all the trails no problem. Suspect your older kids would manage those OK.
Also – it overlaps the Beast for a bit, so my lad came away telling everyone how he rode a chunk of a black trail, still thinks he’s a legend.