All three were about seventh grade, I'd say. And they were all try to sing above their natural range (which was probably alto). They were all nervous, which tightens up one's throat and robs one of breath support. Anyone attempting to sing at the extremes of one's range really needs to get the butterflies out before stepping up, but that's not the only problem here.
All three were singing religious music written in the pop music style. Most pop music is written too high for the average singer to comfortably sing. This is not a new problem. If these youth want to sing along with Amy Grant, my generation sang along with John Denver. We're in soprano/first tenor range here. Even John Fogarty of the old CCR may have sounded all gravelly baritone, but the pitch he was singing at was pure tenor. The person working with them needs to help them identify songs within their range, or work to lower the key.
Unfortunately, you can't lower the key on karaoke. And that's not the only problem with recorded accompaniment. The great advantage to a live pianist is that the notes struck resonate in one's skull, making it easy to match the pitch of the instrument. Singing to electronic music (especially the tinkly, shimmering sound of many pop pieces) is very difficult. You have to be really comfortable hitting your pitch.
So, kudos to the kiddos. I appreciate your moxie. You survived the performance, and that's the first priority. But to the teacher, I'd say: You can help them do better by guiding them in their selection of performance pieces and arranging for live accompaniment. If I were directing them, that's what I'd do. And when they have more satisfying results, they'll have the confidence to attempt more and greater than they did before.