You are welcome to add the Park Hopper option or the Water Park Fun & More option (or both) to your base ticket at any time you are at WDW. Simply go up to any ticket window or guest relations office and tell them that you'd like to upgrade your ticket.
If you do want to do this, you should do it early in your trip. The Park Hopper add-on costs one flat fee, regardless of the number of
ticket days you have. Prices can change, but currently, the Park Hopper
costs about $50. This same $50 is applied whether you are adding the Hopper
to a one-day ticket or a ten-day ticket. If you think you want to Hop
at all, you should purchase the Hopper option early in your trip, so
that you have the most possible flexibility in your vacation. There is a similar situation with the Water Park option.
Whether to get the Hopper or the WPF&M, or both, really depends on the interests of your family. My girls (age 13 and 9) LOVE the water parks. We make it a point to visit at least once during every trip. However, I will say that we didn't even try the water parks until they had been to WDW almost a dozen times. Initially we were so busy exploring the theme parks, that we didn't feel the need to branch out. Also, some people don't like to visit the water parks unless the weather is in a very specific zone. You may want to consider how weather would impact your enjoyment of the water parks.
The WPF&M option includes admission to Blizzard Beach, Typhoon Lagoon, DisneyQuest, or a round at Disney's 9-hole Oak Trail golf course. 18-hole rounds at the major courses are not included.
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