Anterior Cruciate Ligament (ACL) Tears: Although less common in young children, ACL injuries can occur due to sports or high-impact activities. ACL tears often lead to significant instability, especially during activities that involve pivoting or cutting movements.
Medial Collateral Ligament (MCL) Injuries: These can happen due to a direct blow to the outer side of the knee, leading to instability, particularly on the inner side of the knee.

Patellar Subluxation/Dislocation: The kneecap (patella) may partially or completely slip out of place, leading to a sensation of instability. This is more common in children with loose ligaments or abnormal knee alignment.
Patellofemoral Pain Syndrome: Often associated with maltracking of the patella, this condition can cause discomfort and a feeling of instability, particularly when going up or down stairs.

Torn Meniscus: A meniscal tear, though less common in young children compared to adolescents and adults, can lead to knee locking, swelling, and instability. These injuries often result from twisting movements.

Physeal (Growth Plate) Injuries: Children have growth plates that are weaker than the surrounding ligaments and bones, making them susceptible to injury. Damage to the growth plate can lead to instability if not properly treated.

Congenital Knee Dislocation: A rare condition present at birth where the knee joint is abnormally aligned or dislocated, leading to instability.
Ehlers-Danlos Syndrome (EDS) or Other Connective Tissue Disorders: Conditions that affect collagen can lead to overly flexible joints, including the knees, causing instability.

Septic Arthritis: An infection in the knee joint can lead to instability, pain, and swelling.
Juvenile Idiopathic Arthritis (JIA): This condition can cause inflammation and damage to the knee joint, leading to instability.

Any significant trauma to the knee, such as falls or direct impacts, can cause ligamentous injuries, fractures, or cartilage damage, all of which may contribute to instability.