What should we aware of before marriage?

Awareness is a higher stage of knowledge in its
evolutionary progress towards wisdom.(Vethathiri Maharishi)

To make a kid/child healthy parent's body & mind should be healthy. It's like how soil should be in very good condition for seeds to germinate.

Playing (sadana sargam) Suktas From The Atharva Veda , Arutperum Jothi Agaval, Vishnu Sahasranamam, Gayathri Mantra and hearing good speeches was effective. Idea was to bring out the full potential of kid. So it was started when he was fetus.

After baby was born musics were played to make him sleep.

After birth mother should have healthy food to feed the kid.
After 6 months kid should have proper/healthy solid food. So parents should be more aware of what is required in life.

Becoming pregnant should not be an accident. It should happen in higher awareness not with complex emotions.

After 3 years kid should be admitted to a school where they will bring out his/her full potential.

If foundation is good, building will be strong.

If parents don't have any awareness then don't teach kids. Main issue is if parent is aware that he doesn't know anything.