The number of knee injuries in young children has risen sharply in recent years, due to more intensive participation in sporting activities by children at an increasingly lower age. This has led to more anterior cruciate ligament (ACL) ruptures. An ACL rupture has major consequences for the young athlete, but diagnosing this injury in a child can be difficult due to pain and anxiety. The criteria for appropriate treatment of an ACL rupture are not always clear for the child, the doctor, the parents and the sporting coach. Here we describe the diagnosis and possible treatment options for an ACL rupture in children based on three cases. We conclude that the incidence of ACL ruptures in children is a growing problem. There is a challenge for sports associations, sports clubs, trainers and parents to build in prevention programmes during weekly training sessions. The considerations to be taken into account concerning diagnosis and different treatment options show, once again, that children cannot simply be considered as small adults.