To make sure your child only receives messages from people they trust they can block, delete or report users.
Delete or block users
Blocked users will not be able to contact you. Any updates to your status, profile image and last seen timestamps will not be shown. If you have blocked someone, they will not be notified but may still be able to work it out as your status message will no longer be displayed.
Please note that blocking will not remove the contact from the WhatsApp list nor will it remove you from the list on this contact’s phone. To delete a contact in WhatsApp you must delete the contact from your phone’s address book.
If you receive a message from an unknown contact you can Report spam and Block. This will report the user and add the user your Blocked list.