Cruciate ligament tears in children used to be very uncommon, but they are becoming more common as children participate more in demanding sports.
The issue of such injuries in children is that their bones are still growing, with special regions towards the ends of long bones ('growth plates' or 'open physes') having very actively-dividing cells. When a child becomes an adult, the cells in the physes stop dividing and are said to 'close'.
Surgeons are likely to be reluctant to do a cruciate ligament reconstruction on a child before the physes close, leaving the child vulnerable to ongoing knee instability and secondary damage to the meniscus or the joint cartilage surfaces. The reason for the reluctance is that any tunnels drilled through the bone to accommodate the graft are likely to go through the physis, and this may arrest growth or cause bany deformity. So the decision of whether to operate or not is a difficult one, and different surgeons will have different opinions on this. It is best to consult a surgeon who has a special interest in working with children.