The legal and logistical pitfalls in what you propose are not minor, but it's going to take some serious salesmanship for these kids' parents not to run you off the property. What you're looking for is an entrepreneurial-minded, self motivated, self directed high school kid to provide all the equipment, all the labor, and essentially their own route management. By the sounds of it you're not providing any tools, any protection in terms of insurance, and the "training" you provide is... a binder? What are you bringing to the table to justify your cut of the revenue? If it's the accounts, any kid who's your ideal subcontractor (calling them employees is a misnomer) could canvas a neighborhood and get all the work he or she wants.
It's been a while since someone came on here with an idea for how to build a lawn care empire while never getting dirt under his nails, it's about time!