Knee pain in three-year-old toddlers may be related to trauma, calcium deficiency and other factors, which need to be further examined. 1. Trauma: knee pain in toddlers may be related to trauma, such as playing with other children, being pushed down and falling and hurting the knee, this pain will improve after rest. 2. Calcium deficiency: A lack of calcium and vitamin D in a toddler’s body can also lead to the above situation, and may also be accompanied by night terrors and other undesirable phenomena. 3. Growing pains: knee pain in three year olds can also be associated with growing pains, which are mostly transient and can improve on their own without affecting their activities. There may be other reasons for knee pain in three-year-olds. If proper rest does not improve the condition, you need to go to the hospital for a CT scan to find out if there are any fractures or ligament strains, so as to avoid delaying the child’s condition.