This is when the top portion of the leg, or femur, rotates inward too far. If your child sleeps on his belly, with his legs tucked under him, and his bottom up in the air, this can also further internally rotate the leg. This usually affects the portion of the leg below the knee. When the lower portion of the leg is abnormally rotated inward it is called tibial torsion. The tibia is one of the bones in the portion of the leg below the knee.
Torsion is just what it sounds like.
The bone is actually twisted slightly, causing the feet to point inward. The top part of the leg is normal in tibial torsion. The final area that can cause pigeon toeing is the foot itself. When your child walks, the back half of his foot may be completely straight. But the front half may be curved inward.