Most markers systems use foam or dye. Markers by abe continuous but are usually intermittent - about every 25 feet. The foam or dye requires a separate tank and mix, a pump or compressor, a delivery to each end of the boom, and a control to select the desired boom end. No endorsement is intended by Iowa State University Cooperative Extension Service of companies or their products mentioned nor is criticism implied of similar companies or their products not mentioned. Many pesticides are so toxic that exposure to even a small amount can kill and adult.
Children can succumb to less.
Minimize any kind of oral, dermal, or inhalation exposure to chemicals. Below are just a few safety precautions. Read the sprayer operator's manual and chemical labels to review recommended procedures for safe use of chemicals and the equipment. Never allow them to play in pesticide-treated fields or in areas where the chemicals may be spilled. This includes ares where runoff or drift may be present.