The process revolves around a child's drawing. Each part of each drawing corresponds to a score as in the Draw a Person Test conceived by Dr. Florence Goodenough in 1926. The goal of the machine is to measure a child's mental age through a figure drawing task.
That's a very nice challenge!
As always, the hardest part is to get a labeled database (maybe by scrapping).
You'd probably need some thousands of drawings and their respective drawer age.
From there, you need to make an image regression model. Here is a simple example that predicts age from a face photo. It's the same principle, but applied to another database, with other relevant features to be learned by the model.