I'm not 100% certain, but I think so. Quantities of bikes with child seats may be limited, though. I know they have bicycle pedicabs/drivers up there as well. Make sure you bring enough cash for the deposit (RMB 300?) and the rental itself (RMB 40 for 100 minutes, IIRC). And don't pick a day that is too cold, too hot, too windy, or too smoggy! Use one of the major entrances to the wall (maybe the South Gate) where there is the largest stable of bikes available--your hotel should know which entrance is best.