Why can it be difficult to match the identification of baby pictures with those of adults?

The shape and size of the face, whether in regard to appearance or expressions, the baby pictures shows quite and sometime drastic changes when the same baby enters adulthood.

Explanation:

It is very difficult to match the baby pictures and adult pictures of the same person. The quickest changes occurs during infant age to 3 years of age  and during childhood to adolescent period. These are in respect to facial and cranial features along with shapes. Also the texture and skull to skeletal length ratio changes dramatically. Changes occurs in physical, behavioral, psychological aspects and genetic expressions too when an individual grows up to adulthood. In the baby pictures, the eyes are bigger in comparison to face, the face is more plump and round, eyebrows are generally short, nose too is short and small. The teeth which was missing in baby face gradually appear in adult, nose becomes wider and  elongated and the face becomes distinctive with flattening and well demarcation of cheeks. Finally secondary sexual characteristic appears with facial hair, beard or mustache in male. Also there is thinning of  soft tissues of face and prominence of bony structure with adulthood.

we would need to see the picture to answer it