"Kinder, liebe Kinder, es hat mir Spaß gemacht." From https://en.m.wikipedia.org/wiki/Sandm%C3%A4nnchen
Here, Kinder is nominative plural: die Kinder. So, one would say "Die Kinder sind liebe" I would expect "Lieben Kinder sind..."
Is there a reason for this or is it just some poetic license?