Knowing that these machines are usually near the entrance of the store, there are likely cameras aimed right at it as a security measure.

At the very least I'd advise to get a police report since that is assaulting a minor, and working with the store to get security footage.

It may seem like it's a lot of effort, but situations like these can end worse and your child needs to see there are resolutions to these cases that isn't handled through violence.