First, it’s sweet that you’re learning to help children with their assignments haha – and math at that! Kudos.

When adding fractions, the number below – called the denominator, should be equal. So, this problem is simple since the denominators are already the same.

It’s just
1/3 + 1/3 = 2/3

Basically, just find the lowest common denominator (list the multiples of each denominator and find one that matches), but don’t add them, just the numerators (the number above). If needed, you can simplify the fraction by determining the greatest common factor between the numerator and denominator and divide both with that number.

For example
8/24

Factors
8 = 1, 2, 4, 8
24 = 1, 2, 3, 4, 6, 8, 12, 24

Their greatest common factor is 8.

So,

8 ÷ 8 = 1
24 ÷ 8 = 3

= 1/3

Hope this helps!