Not remotely uncommon to find out the second income brings little to no real gain to the family bottom line in many cases... and can sometimes even hurt it... by the time like you realized, you take into consideration, taxes, day care, commuting, clothing, food etc etc.
Let alone the incalculable cost of someone else raising your children.
Since that time I have become close friends with the mother of my daghter's best friend, we have become each other's childcare provider when the need arises.