All baptized children who die before the age of seven will go to heaven.
Oh, that magic number of 7. I'm certain there are no children who reach the magical "age of reason" prior to, or after 7, but those who are 7 and are baptized will miraculously go to heaven.
There is really no way of knowing how many souls are in heaven or hell. All of this speculation is worthless, and not part of Catholic doctrine. "Dare we hope that all may be saved?" indeed.