Can the goalkeeper pick up a header from a teammate?

A goalkeeper may normally handle a ball deliberately headed, chested or kneed to them by a teammate. The restriction applies when the ball has been deliberately kicked to the goalkeeper, or received directly from a teammate's throw-in. There is an important exception. A player cannot deliberately create a trick with the head, chest or knee simply to get around the back-pass law. That is an offence even if the goalkeeper never handles the ball. So a genuine header during normal play is fine. Flicking the ball up to head it back as a planned way of avoiding the restriction is not. I would teach the players the football reason first. Use the goalkeeper if it is the right safe option, but do not create artificial tricks to exploit the wording of the law. For the related chest or knee question, a genuine header, chest or knee pass can normally be handled. The offence is the deliberate trick used to avoid the restriction, such as flicking the ball up to head or knee it back. The referee judges the action and intent, not simply which body part touched the ball.