The Nemco onion slicer is likely not safe for children to use. Nemco is a company that manufactures equipment for the food service industry, and the operations manual for the Nemco onion slicer cautions that the blades are extremely sharp.
Nemco does not appear to intend its products for use at home, as the company's focus is on the commercial food industry. Additionally, while the operations manual for the Nemco onion slicer does not explicitly state that children are not to use the machine, the instructions suggest that it is a powerful machine that individuals should operate with utmost care. It is reasonable to conclude that children should not use the Nemco onion slicer.