Kids. They're still figuring out the world and things like manners and hygiene. It's up to you to keep them healthy and teach them healthy habits. Because, let's face it, kids have some gross habits. It can be difficult for kids to understand the idea of invisible germs that can make them sick, so start explaining early on why sticking their finger in their nose is a bad idea. More importantly, teach them how to wash their hands and keep antibacterial hand soap around. Get those germs off of little fingers before they spread.
Ew. Keep tissues on hand and make your child use one whenever you catch them picking his nose or wiping it on the back of a hand. Explain that it's a habit most people find disgusting and rude and that it can spread germs that will make them sick. Then make sure they go and wash their hands with hand soap.
Kids don’t see the problem with sharing a can of soda, a straw or any of their food with their friends. Even ignoring the problem of dangerous food allergies can be a bad habit that can sometimes spread illness. One way to combat some of this germ-sharing is to get kids in the habit of washing with hand soap before meals. This way they are less likely to spread germs to the food they're eating or passing germs on to others.
Picking at scabs
All children get bumps, scrapes and cuts when they're busy doing what kids do. Some kids can be fascinated with their body's healing process. Convincing them to keep a bandage on the wound and to leave the scab alone so that it heals properly can be a chore. But helping them to wash hands frequently with hand soap and explaining that even small ouches can get infected if we pick at them should help them exert a little self-control. Maybe challenge them to let the scab fall off naturally and take bets on how many days it will take. As with all good hygiene, working with your child to understand that your body needs to heal is the best approach.