My 4'10", 10 year old daughter was on 136 K2 Apache Jrs and Public Enemies last year. K2s measure long compared to other brands. This year, her quiver will add 143 Line Celebrity Minis, and she may move to the 146 Apache Jrs I have waiting in the wings.
My 4'5", 7 year old son will be on 128 Rossignol Bandit Jrs and 131 Fischer Riu Jrs this winter. His 4'2" twin will be on 118 Rossignol Bandit Jrs and 119 K2 Juvys.
For their skill levels, I'd guess that the Bandit Jrs (138s, probably) are an excellent all-around bet in the Rockies. If you can find old-stock 136 Apache Jrs, those would probably be great as well, but you want black ones, not red -- the red are just a renamed beginner/intermediate ski.