First of all these kids are incredibly young. Historically they know who Elvis is, but I bet they don't have a collection of Elvis songs in their heads from which to choose which would best suit their voices and personalities.
The first thing I would have done is to have given each one of them ELvis CDs and told them to listen to him, or at least gotten them together and played some of his songs.
Next, why doesn't somebody give these kids some direction? I am not a musician, but as an educator, I recognized the principle that a previous poster ( who must be one) espoused when that person gave particular songs as being suited for particular contestants.
Why couldn't somebody on the show have said to the contestant: "This is only a suggestion, but these are some examples of Elvis' songs that I think are particularly suited for your voice and style because....."
"You might want to consider staying away from such and such because......"
If each contestant is helped a little in this way, there is no undue favoritism shown. In addition, their efforts will be better showcased, and i will be better entertained - which ostensibly is at least part of the purpose for this show.