Here's what I found from The Traditional poetry of the Finns by Comparetti.

p 145 The fundamental rune is the Son of Kaleva's' (or of
Kalervo's) Vengeance. This rune may be said, in a certain
sense, to be double, for it has two very different forms; with

146 this in common, however, that they both treat of ven-
geance. One relates how Kaleva's son, soon after he was
born, rent his swaddling bands, broke his cradle, etc.; how
he was sold to a smith whose wife used him as a shepherd
and gave him a loaf with a stone inside, and how he re-
venged himself by killing her.