Use them as a tool! Engaging with your child about their imaginary friend can be a great way to get them to open up about experiences they might otherwise be reluctant to share and to talk about feelings they aren't otherwise ready to communicate. Your kid might not want to admit to having a tough day at school or being nervous about meeting a new baby brother, but he might be open to talking about how his invisible friend is reacting to both.
While the general rule of thumb is to accept your child's imaginary companion and incorporate them into your family life, it's fine to challenge your kid if their friend becomes disruptive (i.e. demanding to sit in their sister's car seat or order their own pricey meal at a restaurant) or if they're using their faux friend to take the blame for their own actions. No matter who made the mess, your child is still responsible for helping to clean it up.
