I think SW is a great park at those ages, the kiddies play area has some fun things for them to do and they'll love the shows.
The 5y old has a chance, I think, of being the right age to be asked to take part in the Dolphin show ( if they're still using the same format). It's worth getting to the stadium 30-40 minutes before the show ( let the kids use it as a drink/icecream rest break. You will often see a CM wander about at the front of the glass at the front of the dolphin pool with a clip board ( it has the paperwork that has to be signed by parents to "release" their child to take part in the show). This CM has the job of selecting the child for that show, if you can prompt ( or take) your child to ask the CM some questions ( what's the dolphins names, what do they feel like, what do they eat etc) the CM is likely to ask if they would like to meet the dolphins and be in the show. Obviously they like kids that show an interest in the animals but also kids that show a little independance/confidence. It also helps if the girls are dressed in something pretty (any one who's seem the show is likely to know the "joke" and why it works best with a pretty dress). Most of the CMs are just happy to have a kid that shows an interest, if they can get the job done quickly and dealt with they are happy to get backstage ASAP.
Both my DD's were lucky enough to be in the show at different times and it's a real treasured memory. Obviously there are a lot of kids about so it's by no means certain, but with a little planning you can shorten the odds a good deal.