I want to know what is the difference between [the] following types of esotropia (strabismus):
                       1. Infantile Esotropia
                       2. Essential Esotropia
                       3. Infantile Esotropic Syndrome

Are they all different or [are they the] same?

Each of these terms is describing the same clinical entity. This is:

Esotropia present by 4 months of age in an infant with otherwise normal eyes and motility (in Ciancia syndrome with cross fixation, abduction will apparently be diminished, but it becomes full when one eye is patched). In my experience, all patients have optokinetic asymmetry.

For a full explantion, go to: E-Resources > Ophthalmology Books and Manuals > Surgical Management of Strabismus and read the section on "Congenital Esotropia". This effort will be worth your time if you are interested in learning more about congenital esotropia. You will also be able to learn from the E-Learning strabismus course by studying the lecture on congenital esotropia. Dr. von Noorden's book, Binocular Vision and Ocular Motility also found on the website under Ophthalmology Books and Manuals is another excelllent source.