so that leaves 2/7 and 7/32. What is the easiest way for a 10 yr old to compare these two?
2/7 is more than a quarter (2/7 > 2/8, because a/b > a/(b+n) for a positive n).
7/32 is less than a quarter (7/32 < 8/32, obviously).
You will have to find the LCD (lowest common denominator)
I'd be surprised if that's the intended route to it. 5.7.32 is hardly a five second job to work out by hand, and there's a lot of primes floating around in the question to make it long-winded to do.
I think it's significant that 7/32 is the only one that's less than a quarter. if you just multiply the numerator in each fraction by 4, it's greater than or equal to the denominator in each case (4/4, 12/8, 8/5, 8/7) other than in the last (28/32). So 7/32 is the smallest.