The rule that I would change in hockey is to let kids start checking as mites. The reason for this is to ensure that the kids are familiar with checking before they are so big they can seriously hurt others. This needs to be paired with some serious couching of the kids to ensure they know how to hit the correct way. They also need to be taught how to take a hit correctly. Without learning both of these skills at a young age they are more at risk if they are introduced to checking when they are older. When they are older the size difference between the kids can be greater due to some going through puberty earlier. This means there is a huge chance a bigger kid who doesnt know how to safely check. Seriously injure a smaller player by not hitting them correctly. This can be reduced with proper training and coaching but doing this earlier when the players are smaller and not a strong will prevent severe injuries later.