I still think "cria cuervos y te sacarán los ojos" is more "You can take an animal out of the wild, but you can't take the wild out of an animal" that really "Bring your children up badly and you'll suffer for it" or "when you do sth in good faith and the other doesn´t thank you"
For me it has an old meaning of "what's natural it's natural", or that the effects of education are only in the surface"
The best example it's the scorpion fable
http://en.wikipedia.org/wiki/The_Scorpion_and_the_Frog
I also love a spanish sentence, refering to a good weapon or a good ham knife (cuchillo jamonero)
"cuidado con éste que no conoce ni a su padre"
Saludos
