25% of the children like blue, so 0.25*32 = 8 like blue. This is the same number of people who like orange.
So you'll have "blue" in one quarter slice and "orange" in another quarter slice.
So far, we've counted 8 blue + 8 orange = 16 total. Because there are 32 kids overall, this leaves 32-16 = 16 left. This matches up with the fact that 16 like red. This is half of 32, meaning we'll shade two quarter slices to indicate red. Put another way, you'll have "red" in two slices.
Check out the diagram below. That's one possible configuration (other combos are possible).