IMHO SeaWorld handles crowds better than any other park in Orlando. If you're not planning to go on the rides you should be able to cover pretty much all of the rest of the park in one day. It might require some pretty tight timing between some of the shows because there are a lot of them. IMHO you're likely to have to miss at least one shows. I would suggest a stroller if possible, there is quite a lot of walking about. At 5 I think they will need it for maybe an hour each.
Don't forget , even at Xmas, they often run second day free programs. If you can find an extra half day in your itinerary, you would be able to fit in anything you missed. I think they are still running the "Florida Fun Pass " promo on their website. Pay for one day's entrance and you get unlimited entry up to the end of Dec 2002. I do think that with the amount of fun passes sold to locals that SW ( and BG) might find the end of the year goes a little quiet for them in December as many people will have had their fill of those parks. The other side of that coin is that people will have tickets they have paid for and decide to use them anyway, it's a tough one to call. I would certainly try to avoid both SW and BG at weekends if you have the choice. IF they get busy with locals using up the last of their cheap passes, it will be at weekends JMHO