[Songman45]

If the intent is to get pics of the kids at an amusement park far reach isn't going to be your friend anyway. Keep in mind there will be a crowd and every step you have to take away from your subjects is a step that will fill with a potnetial obstruction. Remember also the distance can impact your getting their attention. Telephoto will have the tendancy to narrow the field of vew and will omit the expanse. I would choose something in the medium wide through long normal reach for focal lengths. 28 [now 24] - 70 or 28-105 to me would be a good walking around lens for a theme park. The narrower the range of zoom, the better for optic quality. I think 200mm is a bit long for the situation and 18-200 is an awful wide spread, too heavy on the long end where the results are going to be most compromised.

Steve