GtrGuy - they are both on small 26" frames modded to 24" wheels. Higher bb frames with shorter cranks. Girl is on a Banshee Wildcard - got a new old stock frame for $300. Boy is on a Norco 4XXX - got a barely used frame for $250. Working well, as the girl likes the more plush ride of a more freeride style frame and the boy likes the firmness of the slopestyle type frame, as he really likes the jump trails and dirt jumps.
Hermes - hard to pick a favourite trail. They were so diverse with lots of good. We sought out the interwebz and local knowledge for the "3 best" of each area that the kids' could also handle, so there was not really a lemon in the bunch. Some more fun than others however!
Bend - Tiddleywinks - esp. with all the work they've done on the middle section.
Tahoe - been there a couple times and still love Armstrong Pass to Mr. Toad's. Bang for buck, it's hard to beat VanSickle.
Northstar BP - a great park overall. Gypsy wins.
Mammoth BP - a huge ranging park with as many climbs as descents, but big long epic descents possible. Twilight Zone or Pipeline.
Santa Barb - no favourite… pretty average and I found the network disjointed and harder to coordinate.
Santa Cruz - Demo Forest is the key riding place (yes, there are other more secret locations, but I don't know them)… of Demo, Braille wins. Climb in and climb out, however.
Sandy - Flying Monkey.