IMO, if it were going to be your one and only trip, I would go at 7 and 5. If you plan on a trip every 2-3 yrs (as we do), I would say 5 and 3. We took my son at 3 1/2 and he had a ball and talks about DW constantly 2 months later. However, I plan on us going back next year or the year after. If this were going to be our only trip I would have waited until he was 5.