I very much second Steve C's recommendation to check out Cottonwood Lakes. The hike in is nice and high, but also gentle and extremely beautiful with almost countless fishing spots. And having successfully summited Whitney with two kids starting out at Horseshoe Meadow, it is a great way for both you and your kid to get familiar with the first part of the route around to the back side of Whitney, which, by the way, would be my strong recommendation for tackling Whitney with kids. Feel free to PM for advice on the kid angle, if you would like any. And good luck!
