Same issue here. Just bought a bike off the shelf at a local store and it had grip shifters. My daughter is almost 10 and still has issues with it, even while pedaling. We leave it on the middle chainring up front now, and I just have her go through the cassette in the rear. So her 21 speed bike is effectively a 7 speed until her hands get a little more strength. If she absolutely needs the lower gears, she can shift down, and then I'll shift it back up for her when we get to the top of the hill.