There is no one answer to this question as each situation is unique. However, there are some general warning signs that may indicate your child has been brainwashed. These can include changes in behavior, such as becoming withdrawn or aggressive, sudden changes in beliefs or values, and a loss of interest in activities they used to enjoy. If you notice any of these red flags, it's important to have a conversation with your child to see what might be going on. Additionally, if you're concerned that your child is being subjected to brainwashing by someone else, such as a cult leader or abusive partner, it's important to seek help from a professional who can assess the situation and provide guidance on how to best protect your child.