You don't have to know everything

As they grow, you grow

One of the most comforting things about becoming a mother is that you don't have to know everything at once.  Unless you adopt or marry into an established family, you start out with a little bundle who's needs aren't complicated.  He doesn't know you're an amateur at this parenting thing so you can grow into your new role without fear of comparison.  It doesn't take long before you are comfortable with feeding, bathing, changing, soothing, and understanding your baby's uniqueness.
And before you know it, you're teaching him how to walk, feed himself, toilet train and other more "advanced" skills.  And so it goes...as your child grows, you grow too, all the way to adulthood.  You'll make mistakes along the way but you'll learn from them and find methods that work for you and your children.

So, don't project your worries into the future.  When the future becomes the present, you will be ready for the challenge...even the teenage years.  :)