I have heard more than I can count express regret at having children. Though it is usually in the form of regretting the timing (too young) with a caveat that the regret does not diminish their love.
I would say that it's one thing to regret that you could not do something, and another to regret that you had children. It's a matter of opportunity cost. If I have two events I'd like to attend that are at the same time I can regret not attending one whilst enjoying the one I did attend.
