Johnny was potty trained 2 years ago and for over a year he never had a bathroom accident. Over the last month Johnny has had accidents at least two to three times a week. A month ago is when his parents brought his new baby sister home from the hospital.

It is possible that Johnny would be experiencing what is called "regression". Regression is a behavior that occurs for more than a few weeks, when previously a child wouldn't have been having these issues anymore (such as when a child is already known to be potty trained but reverts back to having accidents fairly frequently). The most likely cause would be stress or a medical issue, in this case a young child may find the inclusion of a new sibling to be a stressful change in their lives. The question states that Johnny has been having accidents for the past month, and during that same time period his sister baby sister was brought home from the hospital. The stress of a schedule change for a young child could cause such issues. I hope this helps.