If CO is still on your agenda, might I suggest the Upper Arkansas River Valley from Leadville down to Salida. So much to see and do. Great activities for kids of yours ages. Our 14 and 16 yo nieces love Salida, summer and winter (and they live in a mountain town). Rafting, mountain biking, fishing, ghost towns, scenic drives, and some of the highest mountains in the lower 48. Always my go-to place when we have out-of-state guests with kids. Of course Glenwood Springs and environs is another option, with the Hot Springs Pool, Hanging Lake, Aspen and Maroon Bells, Marble and Redstone, Glenwood Canyon and the paved bike trail.