If my two year old is fully potty trained can she hang out with her older siblings in the kids club?
You can ask but I believe the answer is going to be no. Unless your two year old is within a few weeks of being 3 that is the only time I have heard in the past of someone being able to get them into Adventure Ocean. Again it never hurts to ask, but I would be prepared for the answer to be no.
Keep in mind that in order for a child to be considered fully potty trained for Adventure Ocean they must be able to do everything themselves, including redressing themself. The Staff is not allowed to help in any manner.