Moms seem to have an endless capacity for self-doubt and insecurities about their mothering skills. I won't try to conjecture why that is, but I did see a quote in the New York Times that sums up the feeling quite eloquently.
I am very poorly today and very stupid and hate everybody and everything. One lives only to make blunders.
That's a quote from Charles Darwin in a letter to the Scottish geologist Charles Lyell in 1861. I always find it a little heartening to know that people that have no place being insecure feel just as inadequate as I do. Then I can believe that my feelings are just as illfounded as theirs obviously are.
So take solace my friends, your feelings of inadequacy are no more founded or sincerely felt than that of one of the world's great geniuses.