Oh horror. I believed this until right now. Not exactly literally. I never knew Haeckels strong thesis. But from what I had been told (probably as contracted as "ontogeny recapitulates phylogeny") I still assumed the linearity part to be true. And I passed this wrong simplification on to my children (probably like your father did). So now I have some damage control to do...

Indirect quotes from the cited Wikipedia article:

Darwin's view, that early embryonic stages are similar to the same embryonic stage of related species but not to the adult stages of these species, has been confirmed by modern evolutionary developmental biology.

"Embryos do reflect the course of evolution, but that course is far more intricate and quirky than Haeckel claimed. Different parts of the same embryo can even evolve in different directions. As a result, the Biogenetic Law was abandoned, and its fall freed scientists to appreciate the full range of embryonic changes that evolution can produce—an appreciation that has yielded spectacular results in recent years as scientists have discovered some of the specific genes that control development."