US or abroad? Snow or not?

Have you asked him???

What's your budget? That will have a big bearing on where you might go. Please don't give use nebulous terms like "affordable" or "not too expensive" or "won't break the bank" - without a dollar point of reference those terms are meaningless.

Where are you traveling from and how much time are you willing to spend "in transit" - that too will dictate how far you can travel?

Do you have a particular mode of transportation in mind - drive, fly, ship???

By "end of December" do you mean the week between Christmas and New Years? If so, expect to pay some of the highest room rates of the year if you are going to visit popular tourist areas.

What types of activities interest your grandson? How active are the "grandparents"?

You mentioned "outdoorsy and active" - in December that could mean cold and snowy conditions if you go someplace in the north. Is that OK?

7 - 9 days, warmer to hot weather, $15,000 , plane transportation, week that includes Christmas Day, He loves animals, exploring, basketball, waterslides in pools, shows. He does not particularly like down time with books and naps. We grandparents are gym spinners, walkers, and in relatively good shape.

Thank you for your expertise and assistance!

No snow....out of the country would be more exciting.

African safari? Not sure if the budget would stretch to that.

It will be warmer south of the equator.

Costa Rica?

Costa Rica may be just the ticket - rain forests with lots of interesting wildlife, plenty of hiking, volcanos and lots of historical points of interest. Probably very doable with a $15,000 budget.

Also look at the island of Dominica - it is an ecotourists delight and definitely can be done on your budget.

Also look into a cruise around the Galapagos Islands - you get up close and personal with all kinds of wildlife. It was one of the best trips we have ever done.

Thank you! Is there a best time of year to do Costa Rica or the cruise around the Galapagos? Which cruiseline did you use?

We cruised the Galapagos on Celebrity (96 passenger ship). There's also a 96 passenger National Geographic ship. Those are the two largest that are allowed to cruise in the Galapagos. Others operators use boats holding either 8, 16, or 32 passengers. The Galapogas chain straddles the equator so weather is the same all year round. It doesn't make any difference when you go .

Costa Rica is a little cooler and gets a little more rain in winter months.

How about a beach town in Mexico? Weather's fantastic that time of year. Plenty to see and do for all ages, lots of active outdoor stuff... ziplines, surfing, boogie boarding, etc. Friendly people, good food.

Also your money would go a lot further than say on a Galapagos cruise (which is a l-o-n-g way to go imho for only a 7 day trip).

If not Mexico, Costa Rica or Hawaii are both good ideas.

Typical Galapagos cruise is 7 days plus 1 day travel time to/from US International Gateway Airports for total of 9 days ( within time frame given by OP).

Agee that Mexico is also a viable option.