Frosti, king in Finland.

Basics

Nothing mentioned of father, mother or wife.
Children: Skjalv (daughter) and Loge (son)
Source

The mention of Frosti in Yngligesoga is that he was the father of Skjalf, who was captured by king Agne of Sweden.

He is likely to be a different person than the one mentioned in the Orkney saga (frosti son of Kari).

Quote: "Kong Agne fór med hærskjold over Finland og la det under seg og fikk dyktig med hærfang, han tok Skjålv, Frostes datter, og hadde henne med seg hjem, og likeså Loge hennes bror."

Unverified statements

It's been suggested that Froste is the son of Vermund Frodasson, king in Denmark. No source.

It's been suggested that Frosti may be the same as Frosti son of Kari, mentioned in the Orkney saga. The dates and children don't fit, and no source for the statement is found.

Barn:
Skjålv Frostedatter, född cirka 410, död cirka 522