So, impetigo isn't really something you treat with over the counter products. It typically requires a prescription from a doctor of a topical antibiotic (like a cream you put on) or a pill if it is systemic (through body). It's basically a staph or strep infection of the skin. And it IS contagious. It's important he receive prompt attention (especially since you are mentioning his eye lid involved) but it needs to be a prescription of antibiotics from a doctor.
Also, you CAN prevent impetigo through good hygiene.
Here's a slide show on it https://www.webmd.com/skin-problems-and-treatments/understanding-impetigo-treatment. Good luck to your grandson , sounds like NO fun for anyone!