It would probably depend on your kids and which they'd prefer - Epcot or AK. (Since I'd assume you also want to do MK along with the Studios.) We love the World Showcase and all it has to offer (including the food and the shows) and a lot of the attractions at Future World in the morning so Epcot would be our choice. But AK is fun, as well, if your kids prefer to go there. Could you do a split day on that one day with a Park Hopper so they could see both? In which case I'd probably do AK in the morning (heading to EE first, then KRR and Safari, ending with ITTBAB), and get some FPs for the afternoon at FW and enjoy WS at night, ending with Illuminations. Have fun whatever you decide to do! (PS I have twins, also, and ten was around the age they started to really love Epcot. It's probably our favorite park, or a close second to MK, anyway. It's easy to blow by it, though, unless you really study all the things you can do there.)