You're seeing things. There's nothing there. His waist is where his waist should be. You said Louie. He's the second one from the right. His sister Lilibet is the last one on the right next to him. Her right arm is laying flat against the ground on the grass near Louie's left thigh. Louie's left hand is clenched. He's not holding anyone's hand in his left hand.
Louie's right arm is being held in his mother's left hand. I don't know what you're seeing, but it sure isn't an extra hand, arm, leg, etc.