They don't have to be show quality. They don't even need to be purebred to enter and take them to the show. However, they need to be good quality purebred show birds in order to win anything.
The judges here will write comments on the cage cards. like "Nice!" on a bird that gets a ribbon. Or "wrong color" "bad comb". or "Poor quality" on the cards of birds that are not good quality.
I suspect that a critical comment on the cage card would hurt the child's feelings. For that reason, I recommend that you decide on a breed and invest in a pair or a trio of quality birds. Show birds are not expensive compared to the cost of any other hobby and a trio can provide you with a huge flock in less than a year if you collect eggs and start incubating.