I found the following sentence:
Это мой ребёнок.
I looked up for the word and it returned "a child" or "a baby".
However, it seems that "ребенок" (е, not ё) also returned "a child" or "a baby".
Is there any difference between the two words? How can I differentiate one from the other?
The only difference is the way of writing the word. In modern written Russian it is quite often acceptable to write е instead of ё, especially when there is no confusion in meaning, and ребенок is unambiguous. Read more in related questions: "Using written е instead of ë", "Is 'ё' a distinct letter, or is it just 'е' with a diaeresis?".
е and ё is a equal in most times, but in official documents, passports and other this difference have big value (and make big problems, if in password ё and in other documents - е).
ё used as ligature for йо: ёлка, ёж, тяжёлый (but йогурт, not ёгурт). Also ё used in handwriting.
In books and press uses е for replace ё (simple tipesettings) without losing values.
Ребёнок = Ребенок, there is no difference.
Russian vowels are paired this way:
Letter ё sounds differently from e, they even are not paired. But letter ё just became unlicky for it's look, people are lasy "put dots on the i's". There were modern attempts to exclude this letter from alphabet, and were movements to protect letter ё.
