There IS a shuttle from Cabana Bay to Seaworld and Aquatica and it is FREE.
You need to book it the day before, go to the Resorts main transportation desk and they will give you a ticket. You get picked up from the carpark at the bottom of the escalators that lead to City Walk. You take the Cabana Bay bus to there and then get on the FREE shuttle.
I'd do that rather than the Uber and have done it before. If your kids need carseats and not portable boosters you can't always get an Uber with a carseat, they are easy to get around WDW but harder elsewhere in Orlando and cost a lot more to hire as you pay $10 for the carseat and most of the time the carseat Ubers are Uber XL cars that are even more expensive.
Get the free shuttle, I've used it and it was super easy and convenient.