Pre-crisis Superman fell in love with Supergirl(the shapeshifting blob one, not his real cousin). They had a child, but the multiverse was out of balance and the Spectre sent Supergirl back to her universe, but left the 6 year old child to wander the universe. A 6 year old child with the power of a precrisis Kryptonian. So she would encounter planets and "play", usually accidentally destroying them.