> but I think there is much better way to estimate how kids would affect your happiness: do activities that put you in extensive contact with kids, e.g., volunteer to baby sit for your friends/family, offer to tutor/advise neighborhood kids, and coach youth sports

I strongly disagree that this gives good evidence whether you'll enjoy having kids yourself. I never liked dealing with kids of any age; the experience with my own kids, however, is vastly different, and I really enjoy their company.