Charlie ate 2/3 of his chocolate bar. Kelsey ate
3/6 of her chocolate bar. If the bars were
originally the same size, did the two friends
eat an equal amount of their chocolate bars?

No, they did not. Charlie are more of the chocolate bar

If you were to simplify 3/6, it would equal to 1/2. 2/3 is bigger than 1/2.

Also if you were to make them have the same denominator, multiply the numerator and denominator of 2/3 by 2.

2*2/3*2
4/6.

4/6 is greater than 3/6.