I cannot speak for anyone else but..... I'm still about & I have no objection to your using anything I have posted regarding my recollections of children's rhymes I've learnt or collected. It would be nice to have my name in a list somewhere along the lines of "thanks to the following who posted on mudcat for their help" but I wouldn't get upset if it wasn't.

Songs I've created myself ..... it would depend on the circumstances & like someone else posted if my work was being used to make someone else money I would expect to be specifically asked for permission & acknowledged as the creator.

The type of publication you appear to be talking about I can't see there being much of a problem.