Do you really hear these songs sung at Mass where you live these days? I haven’t heard “They’ll Know We Are Christians by Our Love” sung at Mass since the 1970s. I’m not sure if I ever heard Kumbaya sung at Mass, but we used to sing it around the campfire when I was in Cub Scouts. “Morning Has Broken” predates Cat Stevens by about 40 years. The words were written by Eleanor Farjeon in the 1930s and the melody is older than that. I sometimes hear that same melody used at Mass now, but with different words, “Christ Be Beside Me,” I think.
I have a certain nostalgia for all three, and I like what each one expresses. I know many people more learned than myself say they are not appropriate for Mass, but as I say, I haven’t heard them actually sung at Mass around where I live for many years.