As a parent myself and my wife being a retired lower school teacher, I'd encourage these kids' interest, ideally with their parents involved, but explain a few ground rules. They seem like nice kids. But even nice kids need ground rules, like being sure to close gates, knowing what to feed and what not to feed chickens, when they may and may not come, and how to act around them. And because not everything that people eat is good for chickens to eat, the kids should be taught to check with you first before giving them anything. And definitely not to go in the coop or pen without you. Perhaps if they are responsible and mature enough and you get to know them better, they could be taught and paid (with their parents' permission) to look after the birds if you were away. You don't want either your chickens or the kids to get hurt.