Anthropometric Measurements using AI/ML

Hello guys! This is my first post. I am a beginner in Machine Learning. As of now my interest lies in OpenCV. I am currently working on a project which aims to measure human body using a cell phone's camera. I understand how complex this task can be. Nevertheless, I am looking for some guidance as to narrow my research down to measuring the head circumference and mid upper arm circumference of a child aged between (0-5) years. I will be thankful, if anyone here can put me in a certain direction to achieve this.