ID these books (Children's book about Greek myths, illustrated book of folk songs) from 1960s

[Whack-a-Mole]

@Horatio_Hellpop

From the same period, there was a book of folk songs–music and lyrics–also heavily illustrated in a style combining elements of cubism and rural Americana.

Maybe:

• Fireside Book of Folk Songs

It sure seems to fit your criteria.