Objects can be directly observed without preparation, and the microscope produces an upright image. In that sense stereo microscopes are suitable for uncomplicated nature observation. They are almost as uncomplicated to use as a magnifying glass, but produce higher magnifications.
But much depends on the interest of the individual child and the parental support. some children might be disappointed, if they are not able to observe the cells that they have learned about in school. Some water organisms, sich as certain algae and diatoms are simply too small to be properly seen with a stereo microscope (and require a compound microscope). Some children might also be interested in preparing permanent slides and for this activity compound microscopes are more suitable.
In any case, children might need guidance and support, and this is an issue which should not be overlooked.